How to add a calculated column to a data frame in R

Adding calculated columns is a fundamental data transformation.

With dplyr

The mutate() function from dplyr makes this straightforward:

library(dplyr)

df <- df %>%
  mutate(total_price = price * quantity)

You can add multiple columns at once:

df <- df %>%
  mutate(
    total_price = price * quantity,
    discount = ifelse(total > 100, 0.1, 0),
    final_price = total_price * (1 - discount)
  )

With base R

Base R uses direct assignment:

df$total_price <- df$price * df$quantity

Or with transform():

df <- transform(df, total_price = price * quantity)

With data.table

The data.table package uses a compact syntax:

library(data.table)

dt[, total_price := price * quantity]

See Also

• mutate()
• ifelse()