head() Function in R: How to Get First Part of R Object

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If you have a large dataset to analyze, then it will get really hard to condense a huge dataset that has 30+ columns and have thousands of rows. To solve this problem, you can use either head() or tail() function. It gives you a snapshot of that large dataset. In this tutorial, we will see how to use a head() function with different R data types.

head() in R

To get the first part of the object in R, use the head() function. The head() function returns the first part of a vector, matrix, table, data frame, or function. The head() method in R is a generic function that can be extended in other classes.

Syntax

head(x, n, …)

Parameters

The x is an object that can be a vector, matrix, table, or data frame.

The n is a positive single integer. If positive or zero, size for the resulting object: number of elements for a vector.

Implementation of R head() function

To create a data frame in R, use the data.frame() function. We passed the named vector as an argument, and it returns the data frame. Now, let’s fetch the first three rows of the data frame using the head() function.

df <- data.frame(c1 = c("a", "b", "c", "d"),
                 c2 = c("e", "f", "g", "h"),
                 c3 = c("i", "j", "k", "l"),
                 c4 = c("m", "n", "o", "p"),
                 c5 = c("q", "r", "s", "t"))

df
cat("First three rows of data frame", "\n")
head(df, 3)

Output

   c1 c2 c3 c4 c5
1  a  e  i  m  q
2  b  f  j  n  r
3  c  g  k  o  s
4  d  h  l  p  t
First three rows of data frame
   c1 c2 c3 c4 c5
1  a  e  i  m  q
2  b  f  j  n  r
3  c  g  k  o  s

While using the head() function, we passed 3: a positive integer as an argument, which indicates the first 3 parts or, in our case, its first 3 rows of the data frame.

Using head() function on Vector

If you apply the head() function to a Vector, it will return the number of elements equal to the n parameter of the head() function.

rv <- 1:10
rv
cat("First five integers of vector", "\n")
head(rv, 5)

Output

[1] 1 2 3 4 5 6 7 8 9 10
First five integers of vector
[1] 1 2 3 4 5

In this example, the n parameter of the head() function is 5, which means it will return the first five elements of the vector, which it did in the output.

Using head() function on Matrix()

To create a matrix in R, use the Matrix () function. The dimension of the Matrix is defined by nrow and ncol property.

Let’s create a matrix of 5 X 3 and fetch the first 3 rows of the matrix using the head() function.

rv <- 1:15
mtrx <- matrix(rv, nrow = 5, ncol = 3)
mtrx
cat("Using head() function to get first 3 rows", "\n")
head(mtrx, 3)

Output

     [,1] [,2] [,3]
[1,]  1    6    11
[2,]  2    7    12
[3,]  3    8    13
[4,]  4    9    14
[5,]  5   10    15
Using head() function to get first 3 rows
     [,1] [,2] [,3]
[1,]  1    6    11
[2,]  2    7    12
[3,]  3    8    13

We used the head() function and pass the matrix and number of rows as arguments, and it returns the matrix with the first three rows.

Using head() function on inbuilt dataset

We will import the USArrests inbuilt R dataset and use the head() function on that dataset.

To import the dataset as a data frame, use the following code.

df <- datasets::USArrests

Now, use the head() function to get the first five rows of the dataset.

df <- datasets::USArrests
head(df, 5)

Output

           Murder Assault UrbanPop  Rape
Alabama    13.2    236     58       21.2
Alaska     10.0    263     48       44.5
Arizona    8.1     294     80       31.0
Arkansas   8.8     190     50       19.5
California 9.0     276     91       40.6

As you can see that we only get the first five rows of the dataset.

That is it for the head() function in R.

 

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