How to extract a column of a dataframe as a vector in R

In this tutorial, we will learn how to extract a column from a dataframe in R. We will extract a column as a vector using base R method and then see multiple examples of using dplyr’s pull() function to extract a column from a dataframe.

Getting Ready with Packages and Data

Let us get started by loading tidyverse the suite of R packages.

library(tidyverse)
# check the version of loaded package dplyr
packageVersion("dplyr")
## [1] '1.0.8'

First, let us create a new toy dataframe with three columns using tibble() function. tibble() function creates a dataframe like object called tibble.

df <- tibble(grp = sample(c("g1","g2"), 6, 
                          replace=TRUE) ) %>%
  mutate(id = row_number(),
         counts = sample(1:20,6) ) 
df
## # A tibble: 6 × 3
##   grp      id counts
##   <chr> <int>  <int>
## 1 g2        1      1
## 2 g1        2     19
## 3 g1        3     12
## 4 g2        4     15
## 5 g1        5      7
## 6 g1        6      3

Extract a column as vector in base R

To extract a column in base R, we use the dataframe name followed by `$` symbol and then the column name of interest. In this example, we extract the column, counts, as a vector

df$counts

## [1]  7  5 16 13 11 18

dplyr’s pull() function to extract a column as a vector

If we specify the column name as argument to pull() function, we will get the column as a vector.

df %>%
  pull(counts)

## [1]  7  5 16 13 11 18

dplyr’s pull() function to extract the last column as a vector

If we don’t specify any column of interest to dplyr’s pull() function, it will give the last column in the dataframe, ” (on the assumption that’s the column you’ve created most recently).”

df %>%
  pull()

## [1]  1 19 12 15  7  3

Extract a column as vector using dplyr’s pull() function with column position

We can also specify the position of a column to extract the column as vector. In the example below, we extract the third column from left as a vector from the dataframe by using pull(3) function.

df %>%
  pull(3)

## [1]  1 19 12 15  7  3

Extract a column as named vector using dplyr’s pull()

By providing two column names to pull() function, we can extract a column as a named vector with names from the second name argument to pull() function.

Here is an example, where we extract grp column as a named vector with names of the vector coming from second argument.

df %>%
  pull(grp, counts)
##    1   19   12   15    7    3 
## "g2" "g1" "g1" "g2" "g1" "g1"

Here is an example, where we extract counts column as a named vector with names of the vector coming from “grp” column, a reverse of the previous example.

df %>%
  pull(counts, grp)

## g2 g1 g1 g2 g1 g1 
##  1 19 12 15  7  3