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rdplyrmutate
Chris
Chris

Reputation: 409

dplyr: mutate with data from last column

I want to create a new column with data from the last column of a data frame:

df <- matrix(1:4, ncol = 2) %>% as.data.frame()
df %>% mutate(V3 = .[[ncol(.)]] * 2)

Is there an easier to read and understand expression than .[[ncol(.)]]?

Upvotes: 1

Views: 186

Answers (3)

alejandro_hagan
alejandro_hagan

Reputation: 1023

The answers above are more efficient but out of completeness, you can assign the last column name to a string then reference the name in the mutate function.

If you want to offset from the last column (eg. second to last column) you can insert the offset position in last_col() argument like last_col(1)

library(dplyr)

df <- matrix(1:4, ncol = 2) %>% as.data.frame()

last_col <- df |> select(last_col()) |> names()
  
df |> 
mutate(V3=.data[[last_col]]*2)

Upvotes: 1

razorofockham
razorofockham

Reputation: 78

If using dplyr::mutate() is not a must, you could directly assign V3 after reversing the column order:

df <- matrix(1:4, ncol = 2) %>% as.data.frame()
df$V3 <- 2*rev(df)[[1]]

Upvotes: 2

stefan
stefan

Reputation: 125418

Using across and last_col you could do:

library(dplyr, warn=FALSE)

df <- matrix(1:4, ncol = 2) %>% as.data.frame()

df %>% 
  mutate(across(last_col(), ~ .x * 2, .names = "V3"))
#>   V1 V2 V3
#> 1  1  3  6
#> 2  2  4  8

Upvotes: 5

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