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

dplyr

dplyr pull()

Published

April 15, 2022

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. Extract A Column As Vector in R ### 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 %
  mutate(id = row_number(),
         counts = sample(1:20,6) ) 
df
## # A tibble: 6 × 3
##   grp      id counts
##      
## 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

--- title: "How to extract a column of a dataframe as a vector in R" date: 2022-04-15 categories: ['dplyr', 'dplyr pull()'] format: html: code-fold: false code-tools: true --- 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. ![Extract A Column As Vector in R](https://rstats101.com/wp-content/uploads/2022/04/extract_a_column_as_vector_R.png) Extract A Column As Vector in R ### Getting Ready with Packages and Data Let us get started by loading tidyverse the suite of R packages. ```r 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. ```r df % mutate(id = row_number(), counts = sample(1:20,6) ) df ## # A tibble: 6 × 3 ## grp id counts ## ## 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 `$` symbol and then the column name of interest. In this example, we extract the column, counts, as a vector ```r df$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. ```r 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)." ```r 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. ```r 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. ```r 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. ```r df %>% pull(counts, grp) ## g2 g1 g1 g2 g1 g1 ## 1 19 12 15 7 3 ```