Know your lists – Exercises

Lists (aka recursive vectors) are the main data structure in R. Since lists are omnipresent (data.frames are a special sub-type) having a deeper understanding of them will make for a more enjoyable data analysis and helps avoid bugs.

Solutions are available here.

Exercise 1
Create a list called x with two elements; two vectors of length 1 called a and b whose value is 1 and 2 respectively.

Exercise 2
Add a third vector of length 1 to x, z = 3.

Exercise 3
Turn your list into a named vector called y with only one line of code.

Exercise 4
Create a new list z which contains two vectors, y and another one with 100 random standard normal numbers.

Exercise 5
With one line of code extract the median from each of the vectors in z.

Exercise 6
Create a new list w containing the dataset iris and z, make sure each element is named. Now, using [[]] on w extract the Petal.width vector. Note that the iris dataset is available in R by default, just type iris in the console.

Exercise 7
Remove both a and c from the list x from question 2.

Exercise 8
Create a new list using the following code:

dfs <- list(
  df1 = data.frame(s="a", t=1:5),
  df2 = data.frame(s="b", t=111:115),
  df3 = data.frame(s="c", t=300:310)
)

Using do.call() bind them toegher in one master data.frame.

Exercise 9
Select df2 from the list (dfs) using the following syntax "[["(a, b) with the right arguments a and b.

Exercise 10
Using a similar call as above, make a new data.frame consisting of rows 3:4 from each of the data.frames in dfs.

(Picture by Shaofu Ku)

Related exercise sets:

Spatial Data Analysis: Introduction to Raster Processing (Part 1) Parallel Computing Exercises: Snow and Rmpi (Part-3) Parallel Computing Exercises: Foreach and DoParallel (Part-2) Mathematical Expressions in R Plots: Tutorial Building Shiny App exercises part 3