You can use the str() function in R to display the internal structure of any R object in a compact way.

This function uses the following basic syntax:

str(object)

where:

• x: The name of the object to display the structure for

The following examples show how to use this function in different scenarios.

Example 1: Use str() with Vector

The following code shows how to use the str() function to display the internal structure of a vector in a compact way:

#create vector
x <- c(2, 4, 4, 5, 8, 10, NA, 15, 12, 12, 19, 24)

#display internal structure of vector
str(x)

num [1:12] 2 4 4 5 8 10 NA 15 12 12 ...

From the output we can see:

• The vector has a class of numeric
• The vector has a length of 12

By default, the str() function also displays the first 10 items in the vector.

Example 2: Use str() with Data Frame

The following code shows how to use the str() function to display the internal structure of a data frame in a compact way:

#create data frame
df <- data.frame(team=c('A', 'B', 'C', 'D', 'E'),
                 points=c(99, 90, 86, 88, 95),
                 assists=c(33, 28, 31, 39, 34),
                 rebounds=c(30, 28, 24, 24, 28))	

#display internal structure of data frame
str(df)

'data.frame':	5 obs. of  4 variables:
 $ team    : chr  "A" "B" "C" "D" ...
 $ points  : num  99 90 86 88 95
 $ assists : num  33 28 31 39 34
 $ rebounds: num  30 28 24 24 28

From the output we can see:

• The object has a class of data.frame
• The data frame has 5 observations (rows) and 4 variables (columns)

Using the str() function is an excellent way to gain a quick understanding of a data frame, especially if the data frame is very large.

In practice, the str() function is one of the first functions used after loading a data frame into R, even before performing any exploratory analysis or statistical modeling.

Example 3: Use str() with Matrix

The following code shows how to use the str() function to display the internal structure of a matrix in a compact way:

#create matrix
mat <- matrix(1:15, nrow=5)

#view matrix
mat

     [,1] [,2] [,3]
[1,]    1    6   11
[2,]    2    7   12
[3,]    3    8   13
[4,]    4    9   14
[5,]    5   10   15

#display internal structure of matrix
str(mat)

 int [1:5, 1:3] 1 2 3 4 5 6 7 8 9 10 ...

From the output we can see:

• The matrix has a class of integer
• The matrix has 5 rows and 3 columns

By default, the str() function also displays the first 10 values in the vector.

Example 4: Use str() with List

The following code shows how to use the str() function to display the internal structure of a list in a compact way:

#create list
my_list <- list(A=1:5, B=c(2, 9), C=c('hey', 'hello'))

#view list
my_list

$A
[1] 1 2 3 4 5

$B
[1] 2 9

$C
[1] "hey"   "hello"

#display internal structure of list
str(my_list)

List of 3
 $ A: int [1:5] 1 2 3 4 5
 $ B: num [1:2] 2 9
 $ C: chr [1:2] "hey" "hello"

From the output we can see:

• The list has 3 elements
• The first element has a name of A, a class of integer, a length of 5, and all 5 values are shown.
• The second element has a name of B, a class of numeric, a length of 2, and the 2 values are shown.
• The third element has a name of C, a class of character, a length of 2, and the 2 values are shown.

By just using the str() function, we’re able to gain a full understanding of the structure of the list.

Additional Resources