Lumi5 – AVR / Arduino Wireless Uploader

This article will focus on setting up the Bluetooth 4.0 module, preparing the uploader, and uploading sketches over Bluetooth 4.0

Prerequisites:

This article builds off:

Upload Arduino Sketches to ATtiny85 with UART

The above article will need to be followed to prepare your ATtiny85 and Windows computer.

1. ATtiny85 (or any ATtiny or ATmega chip)
2. Arduino Uno (or compatible, this will be used once to burn the bootloader to the ATtiny85).
3. FTDI (or compatible UART).
4. Lumi (a browser based uploader for TinySafeBoot).
5. Arduino IDE
6. AVRDUDE
7. HM-10 or HM-11 Breakout*
8. 1k Resistor
9. Soldering iron

*Note: There are much cheaper versions of the breakout listed on eBay, but beware, there are many clones which will not work with this project. The one I’ve listed I’ve verified as working. Of course, I always recommend you roll your own breakout :)

Why?

Over-the-air uploading of programs to embedded devices is one of the more useful implementations in the history of embedded hardware. It allows the post-production and delivery of gadgets to have their behavior tweaked in reaction to end-user feedback.

Likewise, the Arduino phenomenon probably needs little explanation in this venue. However, I’ve personally not found many solutions for over-the-air uploading of Arduino sketches which have acceptable trade-offs. This article, along with the preceding, are nothing more than attempts to share what I’ve found.

Overview:

This is simply for those who are curious on how this works, it may be skipped.

This tutorial will show you how to wirelessly upload Arduino sketches to an ATtiny85 over a PC’s built in Bluetooth 4.0 hardware and an HM-10. The concept is fairly simple.

The HM-10 has firmware which allow it to monitor all incoming serial data for AT commands. It can then intercept these commands from the stream, allowing the user to remotely control the behavior of the HM-10. In short, the HM-10 allows you to send a command to send a pin HIGH or LOW.

Now, the TinySafeBootloader is a serial bootloader for the ATtiny and ATmega AVR chip sets (these are the heart of Arduino). The most important difference between the TinySafeBootloader and others is it allows serial control over the bootloader behavior, this allows programmers to write uploader software for it, which is what I’ve done for this project.

To the point, we will wire up an HM-10 and an ATtiny with the TSB bootloader. One of the HM-10’s IO pins will be connected to the ATtiny’s RESET line. This will allow us to send a command to the remote HM-10, sending the ATtiny85 into bootloader mode, upload a sketch over the Bluetooth connection, then send another command to the HM-10 to send the ATtiny85 back into program execution mode.

Setup

Select a Pin

You will need to select a IO pin on the HM-10 to connect the 1k resistor. Any of the pins listed above should be supported.

Solder the 1k Resistor

After you have selected the IO pin you would like to use, solder a 1k resistor to the castellated (the half-via leads) on the HM-10.

A few notes:

This is not as hard as it looks; believe in yourself Flux and a fine-tip iron are helpful, but required Tweezers allow you to work angles. Tacky-putty helps hold the board in place, leaving both hands free to hold components.

Configure the HM-10 Firmware for Remote Uploading

Before the uploader will work, the HM-10 must be set as a peripheral device and remote transmission mode.

1. Connect the FTDI chip to the HM-10 breakout, as shown.
2. Open the Arduino IDE.
3. Select the COM port connected to your FTDI chip
4. Open the Serial terminal
5. Make sure the terminal is set to, “No line ending”
6. Type AT+ROLE0 and hit “Send”. The response “OK+Set:0” come up.
7. Now, type AT+MODE2 and hit “Send. The response should be “OK+Set:2”.

Optional:

1. You can set the HM-10’s baud rate up to 57,600 (it gets iffy above this rate). This allows the bootloader to run more quickly. Here are the commands:
   • AT+BAUD0 = 9600
   • AT+BAUD1 = 19200
   • AT+BAUD2 = 38400
   • AT+BAUD3 = 57600
2. You can change the name of your device using “AT+NAMExxxxxxxx”.

Wire It Up

The following connections will need to be made:

VCC should be 5V

Compile a Sketch to Upload

In the Arduino IDE, write a program you want to upload to your wireless TSB setup. However, instead of using the Arduino to upload the file, we are going to use it only to compile. To do this, go to Sketch -> Export Compiled Binary Then, select Sketch -> Show Sketch Folder. In this folder there will be two .HEX files. You want the one which does not have “…_with_bootloader.ino”. (Since, we already have a bootloader installed on our ATtiny.)

Connect to the HM-10 Module from Lumi5

I’ve provided a web based uploader for TinySafeBoot. A couple of notes, it only works in Chrome on Linux and Mac.

Before attempting to use the uploader, please open Chrome and type:

chrome://flags/#enable-experimental-web-platform-features

To get Chrome’s “experimental” Bluetooth LE web API to work we have to turn it on. Go ahead and select Enable.

Lumi5

Go ahead and navigate to:

• Lumi5

This is the work-in-progress web based TinySafeBoot loader I’ve been working on. The HM-10 uploader is functional, though.

Turn on your HM-10. Select Bluetooth from the dropdown box and hit Search. If all has gone well, then you will see the name of your HM-10 module listed. Go ahead and connect to it.

Now, in the Pin # box, type the pin number corresponding with the pin on your HM-10 which you are using to reset the TinySafeBootloader.

Select the multi-gear button. This should give you a bootloader handshake button. Try it. It may take a couple of tries, but you should see the bootloader respond with the device signature and memory information.

If all went well, go ahead and click the Upload File button. Select the compiled HEX file from the Compile a Sketch step and hit upload.

Cross your fingers. It should respond with tell you it has written the file.

Important: Go ahead and refresh the webpage and reconnect. Once you’ve reconnected, the program you uploaded should be running.

We setup the HM-10 to hold the reset line low when the module is not connected, this is to save power. But it can be frustrating if your unaware of the setup, as it’s difficult to troubleshoot. “Why the heck isn’t the program running!?”

Please, please be kind and provide feedback. This is a work-in-progress, using a lot of custom hardware and experimental code.

List any questions below and I’ll try to troubleshoot ASAP.

Upload Arduino Sketches to ATtiny85 With UART This article will show you how use a two-wire interface (UART) to upload Arduino sketches to the ATtiny85. In short, we will burn the TinySafeBootloader onto the ATtiny85 using an Arduino Uno as an ISP programmer. After the initial burning of the bootloader, we can then program the ATtiny85 with any FTDI compatible USB-to-UART. And very similar steps may be followed to do the same for an ATtiny84.

There are a few requirements and a lot of setup needed:

Prerequisites:

• ATtiny85 / 84, or ATmega328P
• Windows 10
• Arduino Uno (or compatible, this will be used once to burn the bootloader to the ATtiny85)
• FTDI or compatible UART
• TinySafeBoot uploader
• Arduino IDE
• AVRDUDE

Useful Components:

• Breadboardable Push Button
• 220-330 Ohm Resistor
• LED

Why?

Many may ask, “Really, why would I want to go through all this trouble to install a bootloader on an ATtiny85 when it is less trouble just to use the Arduino ISP?” Good question.

This article was not meant to be independent. The entire purpose of the this is to prepare an ATtiny85 (actually, any ATtiny orATmega uCs) for wireless upload of Arduino sketches or AVR binaries.

Step 1: Upload the ArduinoISP Sketch

Upload the ArduinoISP Sketch There are several guides on how to use an Arduino as an ISP:

• Programming AVR with Arduino) (Video)
• Using an Arduino as an AVR ISP (In-System Programmer)

But outline the steps briefly, just in case.

before wiring up the Arduino Uno to the ATtiny85 you will need to install the Arduino ISP sketch onto the Arduino Uno. This is built into the Arduino IDE.

• File –> Examples –> 11. ArduinoISP –> ArduinoISP

Then hit the Upload button. Wire up the ATtiny85 After the ArduinoISP sketch has been uploaded it is time to burn our bootloader to the ATtiny85. Go ahead and wire your ATtiny85 to the Arduino Uno as shown in the image above.

Step 2: Wire Up the ATtiny85 and Arduino

Now the ArduinoISP sketch has been uploaded it is time to burn our bootloader to the ATtiny85. Go ahead and wire your ATtiny85 to the Arduino Uno as shown in the image.

Step 3: Install AVRDUDE

Now, we will need to install WinAVR

• WinAVR Download

Step 4: Burn TinySafeBootloader on ATtiny85

Burn TinySafeBootloader on ATtiny85 Once AVRDUDE has successfully installed, open it by going to the Start Menu and typing

• cmd

This should open the Windows command prompt. Now, let’s make sure AVRDUDE is installed. Type:

• avrdude

And press return. You should see output similar to what’s in the image.

*Please hear my warning* what we are about to do has the potential of brick your ATtiny85. More specifically, if we set the fuses wrong on the ATtiny85 it might render the chip unusable. That stated, let’s take a moment and talk through what we are doing.

At this point our Arduino Uno is setup as an ISP. We plan to use AVRDUDE to tell the ISP to burn the TinySafeBootloader onto our ATtiny85. In the process we will also set the fuses on the ATtiny85. These fuses are bits of memory which tell the ATtiny85 how to act. There are two will need to set to use TinySafeBoot on any ATtiny supported.

ATtiny85 & ATtiny84 (or any other ATtiny supported):

1. SELFPRGEN – must be set to enable flash writes from firmware
2. BODLEVEL – should be set to avoid flash corruption during unsafe device power-up.

If you are following this guide for the ATmega series the fuses need are:

1. BOOTRST – activated lets the MCU jump into the Bootloader section with every hardware reset.
2. BODLEVEL – should be set to avoid flash corruption during unsafe device power-up.
3. BOOTSZ=11 – to reserve 512 bytes for a Bootloader Section.
4. BLB – set to MODE 2 or 3 to protect Bootloader section from undesirable write access by firmware.

If you don’t quite trust me or if you would like to read more about fuses, here’s a great explanation.

• AVR Fuses

The fuse settings will be written to the ATtiny85 when when burn the bootloader by using AVRDUDE. You are welcome to calculate your own fuses using the nifty EngBedded web app:

• AVR Fuse Calculator

However, I’ve provided the two commands you will need for the to program the ATtiny 84, 85, and ATmega328P. Copy the first command and paste it to the Windows prompt. If the command is successful, copy the second command. If both commands are successful, you should now have the TSB setup on your ATtiny or ATmega chip.

AVRDUDE command to upload:

ATtiny85 at 1mhz

avrdude -P COM# -b 19200 -c avrisp -p t85 -v -e -U lfuse:w:0x62:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m
avrdude -P COM# -b 19200 -c avrisp -p t85 -v -e -U flash:w:tsb_tn85_b3b4_20150826.hex
ATtiny85 at 8mhz

avrdude -P COM# -b 19200 -c avrisp -p t85 -v -e -U lfuse:w:0xe2:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m
avrdude -P COM# -b 19200 -c avrisp -p t85 -v -e -U flash:w:tsb_tn85_b3b4_20150826.hex

ATtiny84 at 1mhz

avrdude -P COM# -b 19200 -c avrisp -p t84 -v -e -U lfuse:w:0x62:m -U hfuse:w:0xdf:m -U efuse:w:0xfe:m
avrdude -P COM# -b 19200 -c avrisp -p t84 -v -e -U flash:w:tsb_tn84_a0a1_20150826.hex

ATtiny84 at 8mhz

avrdude -P COM# -b 19200 -c avrisp -p t84 -v -e -U lfuse:w:0xe2:m -U hfuse:w:0xdf:m -U efuse:w:0xfe:m
avrdude -P COM# -b 19200 -c avrisp -p t84 -v -e -U flash:w:tsb_tn84_a0a1_20150826.hex

ATtmega328P at 8mhz

avrdude -P COM# -b 19200 -c avrisp -p m328p -v -e -U lfuse:w:0xFF:m -U hfuse:w:0xDA:m -U efuse:w:0x05:m
avrdude -P COM# -b 19200 -c avrisp -p m328p -v -e -U flash:w:tsb_m328p_d0d1_20150826.hex

ATmega328P at 16mhz

avrdude -P COM# -b 19200 -c avrisp -p m328p -v -e -U efuse:w:0x05:m -U hfuse:w:0xD6:m -U lfuse:w:0xFF:m
avrdude -P COM# -b 19200 -c avrisp -p m328p -v -e -U flash:w:tsb_m328p_d0d1_20150826.hex

If you have any issues, please leave any questions in the comments below.

Step 5: Setup Arduino for ATtiny Boards – 1

Setup Arduino for ATtiny Boards – 1 You will need to add ATtiny board support to the Arduino IDE. This may be done by going to:

• File —> Preferences

Then enter the following into the box marked “Additional Boards Manager URLs:”

“https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json”

Step 6: Setup Arduino for ATtiny Boards – 2

Then go to,

• Tools —> Boards —> Board Manager

Now you have added the additional boards URL there should be an option:

• “attiny by David A. Mellis”

Install this package.

Step 7: Select the ATtiny85

Select the ATtiny85 Now, you should have the ATtiny group listed under

• Tools –> Boards —> ATtiny

Select the processor and speed you are working with, then, type out whatever program you would like to upload. Once you have finished your code go to:

• Sketch —> Export Compiled Binary

Usually, the Arduino IDE takes care of the upload, however, it doesn’t know how to interface with the TinySafeBootloader. This is where the Lumi Uploader comes in.

Step 8: Download the Uploader

Download the Uploader Download my Lumi Uploader (Windows 10). It only costs a bazillion-million dollars; nah, it’s free.

Lumi Uploader

Warning: this uploader is a work in progress. If you would like to delve into the source it may be found here:

Lumi Uploader Source

Eventually, I’ll probably re-write this app for Mac and iOS. But gotta get the bugs outta of the Windows version first.

Step 9: Connect UART IC to ATtiny85

Connect UART IC to ATtiny85 Connect the UART IC to the ATtiny85 as shown.

Step 10: Upload Arduino Sketch to ATtiny85

Time to upload the sketch!

Open the Lumi Uploader Select COM port which your FTDI chip is connected Set the baud rate between 9600-56700 Click”Connect” Then click connect “Connect to TSB” If the chip is found, it will display the information of the connect chip Use the “Open File” to navigate to the binary we exported in step 8 (make sure to select the version that doesn’t include the bootloader). Once the file is fully loaded, click the button “Write File” Congratulations, if all went well your sketch should now be on the ATtiny85! If not, well, let’s troubleshoot:

What happens if you click the “Reset” button? This should send the DTR line low, then high, essentially resetting the ATtiny85 Did you accidentally select the bootloader included version of your binary? Was the correct COM port selected? Often, windows will list Bluetooth bridges as COM ports, which can make it confusing. Did you try lower baud rates? The TSB uses software serial, which doesn’t work too well on higher baud rates. Did I make a mistake? If so, shoot me a line or leave a comment–I’ll do my best.

SQL Case

The SQL CASE function is one of my favorite. The command basically works like if-then command. If you are familiar with if-then commands, then feel free to skip this next bit.

If-Then

One of the reasons we have the amazing devices we do today is because a computer is capable of reasoning. A computer can compare two things and decide which one it likes.

Now, this may sound simple, but it’s actually a subtle miracle. Anyone who has been stuck on the toothpaste isle trying to decide between the 45 kinds of toothpaste probably understands making decisions is difficult. Of course, human decision making and computer decision making are not even on the same level. Humans can make comparisons of all 45 products at once(sort of). Computers, they have to make a decision between two objects, then, two objects, then two objects, so forth, until it has made it through all 45. Fortunately, computers can make these decisions blazing fast.

In computer programming we call this computer decision making process control flow. But let’s write some pseudocode for a little better understanding:

    If (Computer Likes Toothpaste 1) then buy Toothpaste 1

Pretty simple, right? The only thing a computer can’t do is decide if it likes Toothpaste 1 on its own. We have to program it to do that.

Well, this sentence makes sense if a computer is trying to decide to buy toothpaste or no toothpaste, but what if there are more than two toothpaste options? We just create another if-then statement.

    If (Computer Likes Toothpaste 1 Best) then buy Toothpaste 1
    If (Computer Likes Toothpaste 2 Best) then buy Toothpaste 2

Because the computer makes decisions in order it read them, then if it buys Toothpaste 1 then it will not buy Toothpaste 2. However, if he doesn’t like Toothpaste 1 the best, then if he thinks Toothpaste 2 is the best he’ll buy it. Otherwise, he will not buy any toothpaste–which makes sense, computers don’t have teeth.

This is almost everything we need to know about if-then, two more little catches.

First, what do we do if the computer doesn’t like any of the Toothpaste and don’t want him to just give up? We need a way to say, “Look computer, if you don’t like any toothpaste the best then go ask for help.”

In programming this is known as if-then-else statements. They are similar to if-then but with a contingency clause if something goes wrong.

Let’s take a look:

    if (Computer Likes Toothpaste 1 Best) then buy Toothpaste 1
    if (Computer Likes Toothpaste 2 Best) then buy Toothpaste 2
    else Go Ask a Computer Dentist what to buy

Ok, that’s it. Now let’s apply it to SQL.

SQL CASE WHEN

SQL applies if-then logic in several ways. We’ve already looked at the WHERE statement, which basicaly works like an if-then.

    SELECT * FROM data WHERE Name = 'Bob'

See how this could be written as

    SELECT * FROM data IF Name = 'Bob'

But the most likely SQL statement used for if-then-else logic is the CASE WHEN statement.

Here’s an example to be run in R.

library(sqldf)
################### Data DO NOT CHANGE ###########################
peopleDf <- data.frame(PersonalID=c("ZP1U3EPU2FKAWI6K5US5LDV50KRI1LN7", "IA26X38HOTOIBHYIRV8CKR5RDS8KNGHV", "LASDU89NRABVJWW779W4JGGAN90IQ5B2"), 
                       FirstName=c("Timmy", "Fela", "Sarah"),
                       LastName=c("Tesa", "Falla", "Kerrigan"),
                       DOB=c("2010-01-01", "1999-1-1", "1992-04-01"))
##################################################################

peopleDf1 <- sqldf("SELECT *, 
                  CASE WHEN DOB > '2000-1-1' THEN 'Yes' ELSE 'No' END As 'Millennial' 
                  FROM peopleDf")

Here is the output:

The SQL query, specifically the CASE WHEN statement created a column called Millennial, it then went through every person’s date of birth, comparing it. When the query found a person who was born after 2000-01-01 it inserted a ‘Yes’ in the Millennial column. If they were not born after 2000-01-01 then it set the Millennial column to ‘No.’ Nifty, right?

Notice, the ELSE is required to get the ‘No’. Otherwise, the query would leave everyone else blank.

Here’s a few more examples of using CASE WHEN for powerful results.

Using OR with CASE WHEN

peopleDf2 <- sqldf("SELECT *, 
                  CASE WHEN DOB > '2000-1-1' OR FirstName = 'Sarah' THEN 'PersonIsCool' ELSE 'NotHip' END As 'Cool?' 
                  FROM peopleDf")

Using AND with CASE WHEN

peopleDf3 <- sqldf("SELECT *, 
                  CASE WHEN FirstName = 'Sarah' AND LastName = 'Kerrigan' THEN 'Yes' ELSE '' 
                  END As 'Queen of Blades' 
                  FROM peopleDf")

Using SUM with CASE WHEN

Using CASE WHEN in combination with SUM is a great way to get counts of different discrete data. Below is an example of getting total counts of males and females within the peopleDf

count1 <- sqldf("SELECT 
                  SUM(
                      CASE WHEN Gender = 'Female' THEN 1 ELSE 0 END
                    ) As 'NumberOfFemales',
                  SUM(
                      CASE WHEN Gender = 'Male' THEN 1 ELSE 0 END
                    ) As 'NumberOfMales'
                   FROM peopleDf")

Using Multiple CASES

So far, we’ve only covered one if-then statement, but in our example with the toothpaste we could string them together. The same can be done with CASE WHEN.

peopleDf4 <- sqldf("SELECT *, CASE WHEN DOB >= '1980-01-01' AND DOB < '1990-01-01' THEN 'X'
                           WHEN DOB >= '1990-01-01' AND DOB < '2000-01-01' THEN 'Y'
                           WHEN DOB >= '2000-01-01' AND DOB < '2010-01-01' THEN 'Millennial'
                           WHEN DOB >= '2010-01-01' AND DOB < '2020-01-01' THEN 'NotYetDefined'
                           END As 'Generation'
                   FROM peopleDf")

Paste

The paste() in R is meant for manipulating strings of text. You pass it strings as parameters and it returns one string containing all the strings passed into it. Let’s take a look.

greeting <- paste("Hello how are you,", "Bob?")

After running this line the greeting variable contains the following string Hello how are you, Bob?. This can be used by printing the contents of the variable using the print()

print(greeting)

Side note, print() will actually print out anything you pass it to the console. This can be useful when trying to debug code.

Back to our combined strings, notice whenever the greeting prints out there is a space inserted between ‘you,’ and ‘Bob?’, this is done automatically by paste. It will insert a space between every string you pass it, unless you pass the additional parameter sep. This parameter will take whatever you set it as and insert it between the two strings.

greeting <- paste("Hello how are you,", "Bob?", sep = "!!")
print(greeting)

This time print() will display “Hello how are you,!!Bob?” in the console. But, inserting exclamation marks is probably not what we want. Most of the time we will not want paste to insert anything and we can tell it to insert nothing.

greeting <- paste("Hello how are you,", "Bob?", sep = "")
print(greeting)

Print will spit out “Hello how are you,Bob?”. Notice, there is no longer any character between “you,” and “Bob?”.

Paste is a pretty straightforward function, the one last trick is knowing you can pass in multiple strings.

greeting <- paste("Hello", " how are you,", " Bob?", sep = "")
print(greeting)

This will produce the string “Hello how are you, Bob?”. Notice the spaces were inserted manually so the end string is readable to humans.

Dynamic SQL with Paste()

Prepare to have your mind blown. One of the powers of the paste() is building a sqldf string. Remember using SQLdf like this?

library(sqldf)
################### Data DO NOT CHANGE ###########################
peopleDf <- data.frame(PersonalID=c("ZP1U3EPU2FKAWI6K5US5LDV50KRI1LN7", "IA26X38HOTOIBHYIRV8CKR5RDS8KNGHV", "LASDU89NRABVJWW779W4JGGAN90IQ5B2"), 
                       FirstName=c("Timmy", "Fela", "Sarah"),
                       LastName=c("Tesa", "Falla", "Kerrigan"),
                       DOB=c("2010-01-01", "1999-1-1", "1992-04-01"))
##################################################################

peopleDf1 <- sqldf("SELECT * FROM peopleDf WHERE DOB > '2001-01-01'")

This creates the table

This is a dataframe of everyone who was born after January 1st, 2001. This method of filtering data works for a static date. But let’s say you wanted to easily change out the 2001-01-01 with other dates. You could replace the date with a different date, but when that date is in multiple SQL calls it can be easy to miss one. A better way to do it is using the paste(). And remember, everything inside the sqldf() parentheses is a string.

targetDate <- "2001-01-01"
sqlString <- paste("SELECT * FROM peopleDf WHERE DOB > '", targetDate, "'", sep = "")
peopleDf5 <- sqldf(sqlString)

Ok, let’s take this slow, there’s a lot going on. First, we create a variable called targetDate and assign it the string 2001-01-01. Next, we create a complex string using the paste() which looks a lot like a SQLdf string, but instead of hardcoding the date, we insert the targetDate variable. This creates the following string:

"SELECT * FROM peopleDf WHERE DOB > '2001-01-01'"

Which is then inserted into the variable sqlString, which is a string.

Lastly, we pass the sqlString variable into the sqldf() which executes the fancy SQL query. Awesome, right?

Now, if we want to look at those born after a different date, we simply change the targetDate variable and re-run the script.

targetDate <- "1980-01-01"
sqlString <- paste("SELECT * FROM peopleDf WHERE DOB > '", targetDate, "'", sep = "")
peopleDf5 <- sqldf(sqlString)

Sys.Date()

GSUB

Creating Reusable Code

Writing report code which can be reused is critical to being an effective report specialist. By now, hopefully, you see the power of SQL-R, especially around HMIS data. But you may still feel slow. Or have thoughts like, “If I pulled these data into Excel I could manually filter them in 1/10th the time.” That’s probably true. But, after manually filtering dataset after dataset it becomes apparent finding a way to automate some tasks would save many hours in the long-run. Thus, writing an R scripts for routine work would save countless hours of monotony.

However, one problem remains, each task will usually have a slight variation from the one before it. This causes you to write 95% of the same code with a slight tweak for the current project. And that doesn’t save time at all. In the programming world, the 95% code which is the same is known as bolierplate code.

Ok, that’s the problem. The solution? Functions.

A function is nothing more than a section of code you save into a variable for easy reuse.

Defining a function looks like this:

myNewFunction <- function(){
  # Code you want to run goes here.
}

Then, whenever you want to use this code it can be called like this:

myNewFunction()

If you want to pass the function something to use:

myNewFunction <- function(clientDf){
  clientDf$VeteranStatus
}
clientDf <- read.csv(clientCsvPath)
myNewFunction(clientDf)

And the coolest thing about functions is being able to return data. Functions return whatever data is on the last line of the function. This can be a tricky concept, but at its root it is simple.

Here, the clientDf will be returned.

myNewFunction <- function(clientDf){
  clientDf$VeteranStatus[clientDf$VeteranStatus == "1"]
  clientDf
}
clientDf <- read.csv(clientCsvPath)
veteranList <- myNewFunction(clientDf)

The result is then passed back out of the function, where it can be assigned to a new variable.

You may notice, this is similar to a lot of code we have been using. Like read.csv. That’s because read.csv is a function written by the makers of R and included for our use.

clientDf <- read.csv(clientCsvPath)

This is how R has become powerful tool. Many smart people have written sets of functions, which are called libraries. Feel the power of open-source.

Time to give back to community and write some of our own functions

Data Needed

For this work challenge you will need:

1. Client.csv
2. Enrollment.csv
3. Project.csv
4. Exit.csv

The Goal

Write functions which will do the following:

• Join clientDf, enrollmentDf, projectDf, exitDf and return the combined dataframe.
• Make the following columns readable:
  • Gender
  • VeteranStatus
  • DisablingCondition
  • RelationshipToHoH
  • ResidencePriorLengthOfStay
  • LOSUnderThreshold
  • PreviousStreetESSH
  • TimesHomelessPastThreeYears
  • MonthsHomelessPastThreeYears
  • Destination
• Get most recent HUD Assessment per PersonalID
• Filter to clients who are active in programs (except Night-by-Night and Street Outreach projects)
• Write a function to filter enrollmentDf based upon a user defined parameter.

BONUS

• Write a function which returns a list of Chronically Homeless individuals.

For the last function, here’s an example,

clientsWithDisablingCondition <- getSubpopulation(df, "DisablingCondition", "Yes")

The function you’d write would be getSubpopulation(). The first parameter would be the dataframe the user is passing into your function. Second parameter is the column to look at. The last is which response the user wants in the column to look in.

The Resources

Below are the resources which should help for each step:

• R Programming A-Z – Video 21 – Functions in R
• paste()