You can use the transform() function in base R to modify existing columns or add new columns to a data frame.

This function uses the following basic syntax:

transform(df, my_column = my_column_transformed)

The following examples show how to use this function in different scenarios with the following data frame in R:

#create data frame
df <- data.frame(pos=c('G', 'G', 'F', 'F', 'C'),
                 points=c(23, 29, 33, 14, 10),
                 assists=c(7, 7, 5, 9, 14))

#view data frame
df

  pos points assists
1   G     23       7
2   G     29       7
3   F     33       5
4   F     14       9
5   C     10      14

Example 1: Use transform() to Modify Existing Column

The following code shows how to use the transform() function to modify the existing points column:

#divide existing points column by 2
df_new <- transform(df, points = points / 2)

#view new data frame
df_new

  pos points assists
1   G   11.5       7
2   G   14.5       7
3   F   16.5       5
4   F    7.0       9
5   C    5.0      14

Notice that each value in the existing points column was divided by two and all other columns remained unchanged.

Example 2: Use transform() to Add One New Column

The following code shows how to use the transform() function to add a new column called points2:

#add new column called points2
df_new <- transform(df, points2 = points * 2)

#view new data frame
df_new

  pos points assists points2
1   G     23       7      46
2   G     29       7      58
3   F     33       5      66
4   F     14       9      28
5   C     10      14      20

Notice that the new column has been added to the data frame and all other existing columns remained the same.

Example 3: Use transform() to Add Multiple New Columns

The following code shows how to use the transform() function to add two new columns called points2 and assists2:

#add new columns called points2 and assists2
df_new <- transform(df,
                    points2 = points * 2,                    assists2 = assists * 2)

#view new data frame
df_new

  pos points assists points2 assists2
1   G     23       7      46       14
2   G     29       7      58       14
3   F     33       5      66       10
4   F     14       9      28       18
5   C     10      14      20       28

Notice that two new columns have been added to the data frame and all other existing columns remained the same.

Additional Resources