0: Install / Update R and RStudio

Before you do anything else, make sure you’ve got the latest versions of R and RStudio installed!

0.5 Update Language

If you want to change the laguage in RStudio to English, run the following code:

Sys.setenv(LANG = "en")

1: Create and view data objects

Everything in R is an object with a name. Everything you do in R is a function. Let’s create a new object called my.data some experimental data. The data is stored as a text file at the web link https://dl.dropboxusercontent.com/u/7618380/priming.txt

priming <- read.table(file = "https://dl.dropboxusercontent.com/u/7618380/priming.txt",
                      sep = "\t",   # File is tab-delimited
                      header = T    # There is a header row
                      )

You can look at the data using the View() function applied to the priming object

# Show the priming dataset in a 'spreadsheet'
View(priming)

You can get summary information about the data using the summary() function

# Calculate summary statistics of each column
summary(priming)
       id         sex         age            prime         time       
 Min.   :  1.00   f:53   Min.   :14.00   elderly:50   Min.   : 7.200  
 1st Qu.: 25.75   m:47   1st Qu.:21.00   neutral:50   1st Qu.: 9.375  
 Median : 50.50          Median :22.00                Median :10.300  
 Mean   : 50.50          Mean   :22.21                Mean   :10.337  
 3rd Qu.: 75.25          3rd Qu.:23.00                3rd Qu.:11.225  
 Max.   :100.00          Max.   :27.00                Max.   :14.200

2: Calculate summary statistics

You can calculate simple statistics using functions like mean(), sd(), and table()

# Calculate some basic summary statistics of specific columns

mean(priming$age)   # What was the mean age of the participants?
[1] 22.21
median(priming$time)  # What was the median time?
[1] 10.3
table(priming$sex) # How many people were there of each sex?

 f  m 
53 47

3: Plotting

Plotting is super easy in R!

# Simple histogram of age
hist(x = priming$age)

You can customize the look of your plot with additional plotting arguments

# Age histogram with additional arguments

hist(x = priming$age,
     border = "white", 
     col = "salmon",
     main = "Age Distribution",
     xlab = "Age",
     yaxt = "n",
     ylab = ""
     )

Here’s a boxplot:

# Boxplot of times by priming condition

boxplot(formula = time ~ prime, 
        data = priming,
        col = c("skyblue1", "tomato"),
        ylab = "Walking Times",
        xlab = "Priming Condition",
        main = "Walking times by priming condition (Study 1)"
        )

Now a scatterplot!

# Scatterplot of age and time

plot(x = priming$age,
     y = priming$time,     
     pch = 16,             # point type
     col = gray(.5, .5),   # point color
     cex = 2,              # point sizes
     bty = "n",            # remove outer box
     xlab = "Age",
     ylab = "Time",
     main = "Age and Walking times\nStudy 1"
     )

# Add a regression line!

abline(lm(time ~ age, data = priming),
       col = "red", 
       lty = 2, 
       lwd = 2
       )