Referecing numerical column names as variables in R

user_16935119 0
Viewed 139

I have a dataframe where columns are numneri

asd <- data.frame(`2021`=rnorm(3), `2`=head(letters,3), check.names=FALSE)

But when I reference the columns names as variable, it is returning error

 x = 2021
asd[x]
Error in `[.data.frame`(asd, x) : undefined columns selected

Expected output

x = 2021
asd[x]
        2021 
1  1.5570860
2 -0.8807877
3 -0.7627930
r
4 Answers

Reference it as a string:

x = "2021"
asd[,x]
[1] -0.2317928 -0.1895905  1.2514369
user_80399780

Use deparse

asd[,deparse(x)]
[1]  1.3445921 -0.3509493  0.5028844
asd[deparse(x)]
        2021
1  1.3445921
2 -0.3509493
3  0.5028844
user_167291750

A bit more detail: numbers without quotes are not syntactically valid because they are parsed as numbers, so you will not be able to refer to them as column names without including quotes.

You can force R to interpret a number as a column name by asd$2021

> asd$`2021`
[1] -0.634175 -1.612425  1.164135

Generally, you can protect yourself against syntactically invalid column names by

#(in base R)
names(asd) <- make.names(names(asd))
names(asd)
[1] "X2021" "X2"

#(or in tidyverse)
asd <- as_tibble(asd, .name_repair="universal")
New names:
* `2021` -> ...2021
* `2` -> ...2
# A tibble: 3 x 2
  ...2021 ...2
    <dbl> <chr>
1  -0.634 a
2  -1.61  b
3   1.16  c
user_86845510

If the value is numeric, just convert to character with as.character - column/row names attributes are all character values

asd[as.character(x)]
        2021
1 -0.4438473
2 -0.8904154
3 -0.9319593
user_37322710
Related