How to add a variable description in R?

To add a variable description in R, we can use comment function and if we want to have a look at the description then structure call of the data frame will be used. For example, if we have a data frame say df that contains a column x then we can describe x by using the command comment(df$x)<-c("The name of this variable is x"). Now to have a look at it, we can use str(df).

Example1

Consider the below data frame −

 Live Demo

x1<-rnorm(20,21,3.24)
x2<-rnorm(20,5,2.1)
df1<-data.frame(x1,x2)
df1

Output

     x1        x2
1  23.12252  5.085650
2  19.81415  5.180194
3  14.41423  2.756885
4  21.34914  5.714200
5  18.34662  3.814034
6  21.37762  9.538720
7  21.48240  4.838389
8  22.58701  2.185943
9  15.68257  5.084348
10 20.86272  5.732107
11 19.84529  3.430304
12 26.23832  3.684373
13 25.35179  5.001748
14 19.83831  3.393473
15 23.57819  5.057545
16 15.69374  7.442210
17 15.69028  6.722865
18 18.94718  8.046787
19 25.26722  2.776823
20 23.32905  3.561213

str(df1)

'data.frame': 20 obs. of 2 variables:
$ x1: num 23.1 19.8 14.4 21.3 18.3 ...
$ x2: num 5.09 5.18 2.76 5.71 3.81 ...

Adding description of variables in df1 −

comment(df1$x1)<-c("This variable follows normal distribution")
comment(df1$x2)<-c("This variable follows normal distribution")
str(df1)

'data.frame': 20 obs. of 2 variables −

$ x1: num 23.1 19.8 14.4 21.3 18.3 ...
..- attr(*, "comment")= chr "This variable follows normal distribution"
$ x2: num 5.09 5.18 2.76 5.71 3.81 ...
..- attr(*, "comment")= chr "This variable follows normal distribution"

Example2

 Live Demo

y1<-sample(0:1,20,replace=TRUE)
y2<-sample(LETTERS[1:5],20,replace=TRUE)
df2<-data.frame(y1,y2)
df2

Output

   y1 y2
1  0  B
2  1  E
3  0  B
4  1  A
5  1  D
6  0  A
7  0  E
8  1  D
9  0  D
10 0  D
11 0  E
12 0  C
13 1  A
14 1  D
15 0  B
16 0  E
17 1  C
18 0  C
19 1  D
20 1  C

str(df2)

'data.frame': 20 obs. of 2 variables:
$ y1: int 0 1 0 1 1 0 0 1 0 0 ...
$ y2: chr "B" "E" "B" "A" ...

Adding description of variables in df2 −

comment(df2$y1)<-c("This is a binary variable")
comment(df2$y2)<-c("This is a categorical variable")
str(df2)

'data.frame': 20 obs. of 2 variables −

$ y1: int 0 1 0 1 1 0 0 1 0 0 ...
..- attr(*, "comment")= chr "This is a binary variable"
$ y2: chr "B" "E" "B" "A" ...
..- attr(*, "comment")= chr "This is a categorical variable"