How to Select DataFrame Columns by Index in R?

In this article, we will discuss how to select columns by index from a dataframe in R programming language.

Note: The indexing of the columns in the R programming language always starts from 1.

Method 1: Select Specific Columns By Index with Base R

Here, we are going to select columns by using index with the base R in the dataframe.

Syntax:

dataframe[,c(column_indexes)]

Example:

R

#  create a dataframe with 3 rows and 4 columns
data=data.frame(name=c("akash","kyathi","preethi"),
                subjects=c("java","R","dbms"),
                marks=c(90,98,78))

# select second and third column
print(data[,c(2,3)])

Output:

  subjects marks
1     java    90
2        R    98
3     dbms    78

Method 2: Select Specific Columns In The Index Range

We can select by using the index range operator, as shown below.

Syntax:

dataframe[,column_index_start:column_index_end]

where.

• column_index_start is the first index number, and column_index_end is the second index number.

Example:

R

# create a dataframe with 3 rows and 4 columns
data=data.frame(name=c("akash","kyathi","preethi"),
                subjects=c("java","R","dbms"),
                marks=c(90,98,78))

# select first to third column
print(data[,1:3])

Output:

     name subjects marks
1   akash     java    90
2  kyathi        R    98
3 preethi     dbms    78

Method 3: Select Index Column By Excluding Columns Indexes

We can exclude the index columns by specifying in the c() vector with a – sign.

Syntax:

dataframe[,-c(column_indexes)]

Example:

R

# create a dataframe with 3 rows and 4 columns
data=data.frame(name=c("akash","kyathi","preethi"),
                subjects=c("java","R","dbms"),
                marks=c(90,98,78))

# exclude second and third column
print(data[,-c(2,3)])

Output:

[1] "akash"   "kyathi"  "preethi"

Method 4: Select Column Names By Index Using dplyr

The select() function from the dplyr package is used for selecting column by index.

Syntax:

dataframe %>%
 select(column_numbers)

where

• %>%  operator is to load into dataframe

Syntax to import and install the dplyr package:

install.packages("dplyr")
library("dplyr")

Example:

R

# loads the package
library("dplyr")

# create a dataframe with 3 rows and 4 columns
data = data.frame(name=c("akash", "kyathi", "preethi"),
                  subjects=c("java", "R", "dbms"),
                  marks=c(90, 98, 78))

# select 1  and 3 columns
data % >%
select(1, 3)

Output:

     name marks
1   akash    90
2  kyathi    98
3 preethi    78