Data Frame Manipulation
OverviewTeaching: 10 min
Exercises: 10 minQuestions
Data-frames. What are they, and how to manage them?Objectives
Understand what is a data-frame and learn to manipulate it.
Data-frames: The power of interdisciplinarity
Data-frames are the powerful data structures in R. Let’s begin by creating a mock data set:
> musician <- data.frame(people = c("Medtner", "Radwimps", "Shakira"), pieces = c(722,187,68), likes = c(0,1,1)) > musician
The content of our new object:
people pieces likes 1 Medtner 722 0 2 Radwimps 187 1 3 Shakira 68 1
We have just created our first data-frame. We can see if this is true using the
A data-frame is a collection of vectors (i.e. a list) whose components must be of the same data type within each vector:
Figure 3. Structure of the created data-frame.
We can begin to explore our new object by pulling out columns using the
$ operator. In order to use it,
you need to write the name of your data-frame, followed by the
$ operator and the name of the column
you want to extract:
 "Medtner" "Radwimps" "Shakira"
We can do operations with the columns:
> musician$pieces + 20
 742 207 88
Moreover, we can change the data type of one of the columns. Using the next line of code we can see if the musicians are popular or not:
> musician$likes <- as.logical(musician$likes) > paste("Is",musician$people, "popular? :", musician$likes, sep = " ")
 "Is Medtner popular? : FALSE" "Is Radwimps popular? : TRUE" "Is Shakira popular? : TRUE"
Finally, we can extract information from a specific place in our data by using the “matrix” nomenclature
where the first number inside the brackets specifies the row number, and the second the column number:
Figure 4. Extraction of specific data in a data-frame and a matrix.
> musician[1,2] # The number of pieces that Nikolai Medtner composed
We can also call for that data by calling the column by it’s name
> musician[1,"pieces"] # The number of pieces that Nikolai Medtner composed
Complete the lines of code to obtain the required information
Code Information required > musician[__,__] Pieces composed by Shakira > (musician____)_2 Pieces composed by all musicians if they were half of productive (The half of their actual pieces) > musician$___ <- c(,,___) Redefine the
likescolumn to make all the musicians popular!
がんばって! (ganbatte; good luck):
Code Information required > musician[3,”pieces”] Pieces composed by Shakira > (musician$pieces)/2 Pieces composed by all musicians if they were half of productive (The half of their actual pieces) > musician$likes <- c(“TRUE”,”TRUE”,”TRUE”) Redefine the
likescolumne to make all the musicians popular!
Data-frames contain multiple columns with different types of data.