Digital Data Collection - programming extras

Rolf Fredheim and Yulia Shenderovich
University of Cambridge

24/02/2015

Variables

uni  <-  "The University of Cambridge"
uni

[1] "The University of Cambridge"

Paying tax:

#9400 tax free
(20000-9440)*20/100

[1] 2112

#OR:
wage <- 20000
taxFree <- 9400
rate <- 20
(wage-taxFree)*rate/100

[1] 2120

Briefly about functions

plusOne <- function(x){ 
    return(x+1)         
    }

plusOne2 <- function(num){ 
        return(num+1)           
    }

Curly brackets {} include the code to be executed

Normal brackets () contain a list of variables

    plusOne(8)

[1] 9

    plusOne2(10)

[1] 11

  plusOne2(num=5)

[1] 6

  #plusOne2(wrongVar=2)

Simple loops

for (number in 1:5){
    print (number)
}

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

Looping over functions

a <- c(1,2,3,4,5)
for (value in a){
    print (
        plusOne(value)
    )
}

[1] 2
[1] 3
[1] 4
[1] 5
[1] 6

listOfNumbers <- c(1,2,3,4,5)
for (number in listOfNumbers){
    print (
        number+1
    )
}

[1] 2
[1] 3
[1] 4
[1] 5
[1] 6

More loops

a <- c(1,2,3,4,5)
a[1] #The first number in the vector

[1] 1

a[4] #The fourth number in the vector

[1] 4

for (i in 1:length(a)){
    print (
        plusOne(a[i])
    )
}

[1] 2
[1] 3
[1] 4
[1] 5
[1] 6

Functions without variables

printName <- function(){
  print ("My name is Rolf Fredheim")
}

printName()

[1] "My name is Rolf Fredheim"

This is a useless function. But sometimes, if we have many lines of code requiring no particular input, it can be useful to file them away like this.

e.g. for simulations

sillySimulation <- function(){
x1 <- runif(500,80,100)
x2 <- runif(500,0,100)
v1 <- c(x1,x2)

x3 <- runif(1000,0,100)

df <- data.frame(v1,x3)
require(ggplot2)

print(ggplot(df, aes(v1,x3))+geom_point()+ggtitle("simulation of some sort"))
}

Just as this slide hides the code on the previous slide, so the function hides the underlying code.

sillySimulation()

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Inserting variables

Let's hammer home how to use variables

what variables could we add to the function below?

desperateTimes <- function(){
  print(paste0("Rolf is struggling to finish his PhD on time. Time remaining: 6 months"))
}

Name

desperateTimes <- function(name){
  print(paste0(name ," is struggling to finish his PhD on time. Time remaining: 6 months"))
}
desperateTimes(name="Tom")

[1] "Tom is struggling to finish his PhD on time. Time remaining: 6 months"

Gender

we specify a default value

desperateTimes <- function(name,gender="m"){
  if(gender=="m"){
    pronoun="his"
  }else{
    pronoun="her"
  }

  print(paste0(name ," is struggling to finish ",pronoun," PhD on time. Time remaining: 6 months"))
}
desperateTimes(name="Tanya",gender="f")

[1] "Tanya is struggling to finish her PhD on time. Time remaining: 6 months"

Is this a good function? Why (not)?

degree

desperateTimes <- function(name,gender="m",degree){
  if(gender=="m"){
    pronoun="his"
  }else{
    pronoun="her"
  }

  print(paste0(name ," is struggling to finish ",pronoun," ",degree," on time. Time remaining: 6 months"))
}
desperateTimes(name="Rolf",gender="m","Mphil")

[1] "Rolf is struggling to finish his Mphil on time. Time remaining: 6 months"

Days til deadline

require(lubridate)
require(ggplot2)
deadline=as.Date("2015-09-01")
daysLeft <- deadline-Sys.Date()
totDays <- deadline-as.Date("2011-10-01")
print(daysLeft)

Time difference of 190 days

print(paste0("Rolf is struggling to finish his PhD on time. Days remaining: ", as.numeric(daysLeft)))

[1] "Rolf is struggling to finish his PhD on time. Days remaining: 190"

part2

print(paste0("Percentage to go: ",round(as.numeric(daysLeft)/as.numeric(totDays)*100)))

[1] "Percentage to go: 13"

df <- data.frame(days=c(daysLeft,totDays-daysLeft),lab=c("to go","completed"))
ggplot(df,aes(1,days,fill=lab))+geom_bar(stat="identity",position="fill")

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We could put all this code in a function, and forget about it

timeToWorry <- function(){
  require(lubridate)
  deadline=as.Date("2015-09-01")
  daysLeft <- deadline-Sys.Date()
  totDays <- deadline-as.Date("2011-10-01")
  print(daysLeft)
  print(paste0("Rolf is struggling to finish his PhD on time. Days remaining: ", as.numeric(daysLeft)))
  print(paste0("Percentage to go: ",round(as.numeric(daysLeft)/as.numeric(totDays)*100)))
  df <- data.frame(days=c(daysLeft,totDays-daysLeft),lab=c("to go","completed"))
  ggplot(df,aes(1,days,fill=lab))+geom_bar(stat="identity",position="fill")
}

File it away until in need of a reminder

timeToWorry()

Time difference of 190 days
[1] "Rolf is struggling to finish his PhD on time. Days remaining: 190"
[1] "Percentage to go: 13"

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