Create empty columns with mutate, column names from a vector

Question

There is a data frame df containing one column.

df <- data.frame(pseudonym = c("a", "b", "c", "d"))

df
  pseudonym
1         a
2         b
3         c
4         d

Now I like to create empty columns with column names coming from a character vector (df2 and sn).

sn <- c("sn01", "sn02", "sn03")

sn
[1] "sn01" "sn02" "sn03"

df2 should be

df2 <- data.frame(
  pseudonym = c("a", "b", "c", "d"),
  sn01 = NA,
  sn02 = NA,
  sn03 = NA,
  sn04 = NA
)

df2
  pseudonym sn01 sn02 sn03 sn04
1         a   NA   NA   NA   NA
2         b   NA   NA   NA   NA
3         c   NA   NA   NA   NA
4         d   NA   NA   NA   NA

I'm searching for a tidyverse statement somethink like this

df2 <- mutate___(df, ..., sn)

Could anybody help?

A non-tidyverse statement would be `df[,sn]<-NA`. – Maël Feb 17 '22 at 11:13 — Maël, Feb 17 '22 at 11:13

score 2 · Accepted Answer · answered Feb 17 '22 at 11:18

2

It's probably not really in the spirit of the tidyverse, but you can do

df %>% mutate(`[<-`(df, sn, value = NA))
#>   pseudonym sn01 sn02 sn03
#> 1         a   NA   NA   NA
#> 2         b   NA   NA   NA
#> 3         c   NA   NA   NA
#> 4         d   NA   NA   NA

answered Feb 17 '22 at 11:18

Allan Cameron

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What does this `[<-` mean? Is it a function or an operator? – poetspie Feb 17 '22 at 11:22
1

@poetspie in R, operators _are_ functions. `[<-` is the explicit name of the function that is actually called by the R parser when you do `df[sn] <- NA` – Allan Cameron Feb 17 '22 at 11:24
It is same as Mael suggested in the comments, but inside mutate. – zx8754 Feb 17 '22 at 11:27
@AllanCameron Thanks. Is there a documentation about [<- ? – poetspie Feb 17 '22 at 14:06
@poetspie yes - type `?'[<-'` inyour console. – Allan Cameron Feb 17 '22 at 14:27
@AllanCameron When I use `df[, a] <- value` and the column index _a_ doesn't exist, it will be created. I didn't know that, but now. – poetspie Feb 17 '22 at 14:46

Create empty columns with mutate, column names from a vector

1 Answers1