How do I refer to multiple columns in a dataframe expression?

Question

Writing this is clunky:

df$a <- df$b + df$c

Is there a way to do (the equivalent of):

with df:
    $a <- $b + $c

Answer 1

We can use with command

df$a <- with(df, b + c)

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Another option is using attach, which however is not recommended

attach(df)
df$a <- b + c

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Another options with data.table and dplyr as suggested by @SymbolixAU

library(data.table)
setDT(df)[, a := b + c]

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If you prefer dplyr chains.

library(data.table)
library(dplyr)

df %>%
  mutate(a:= b + c)

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There is also forward pipe operator (%<>%) in magrittr package which doesn't require you to assign the object again to the variable.

library(magrittr)
df %<>%
  mutate(a = b + c)

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Another one similar to with is using transform (suggested by @Maurits Evers)

df <- transform(df, a = b + c)