fread: more advanced use
Now that you know the basics about fread(), you should know about two arguments of the function: drop and select, to drop or select variables of interest.
Suppose you have a dataset that contains 5 variables and you want to keep the first and fifth variable, named "a" and "e". The following options will all do the trick:
fread("path/to/file.txt", drop = 2:4)
fread("path/to/file.txt", select = c(1, 5))
fread("path/to/file.txt", drop = c("b", "c", "d"))
fread("path/to/file.txt", select = c("a", "e"))
Let's stick with potatoes since we're particularly fond of them here at DataCamp. The data is again available in the file potatoes.csv (view), containing comma-separated records.
This exercise is part of the course
Introduction to Importing Data in R
Exercise instructions
- Using
fread()andselectordropas arguments, only import thetextureandmoistnesscolumns of the flat file. They correspond to the columns 6 and 8 in"potatoes.csv". Store the result in a variablepotatoes. plot()2 columns of thepotatoesdata frame:textureon the x-axis,moistnesson the y-axis. Use the dollar sign notation twice. Feel free to name your axes and plot.
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Import columns 6 and 8 of potatoes.csv: potatoes
potatoes <- ___
# Plot texture (x) and moistness (y) of potatoes
___