How to refer to columns in a table via a character variable in r?

Question

Probably a fairly simple question, but couldn't find anything specific for it. Lets say I have the following data frame

A
     Hello World
   1   5     6
   2   5     6

If you want to fetch the the values from the Hello column you would usually just do it with

A$Hello

But is there a way to fetch the column values with a predefined variable like this?

col <- "Hello"
A$col

The latter returns NULL for me

score 1 · Answer 1 · answered Apr 07 '19 at 03:57

1

Try A[col]:

## Hello
##   <dbl>
## 1     5
## 2     5

Essentially, just uses another form of indexing. This works because col is a string.

answered Apr 07 '19 at 03:57

ladylala

this was useful, but not using double bracket syntax actually yields a table rather than a numerical vector like A$Hello does. – MikeKatz45 Apr 07 '19 at 04:24
that's true - sorry I didn't completely think through what you might want (i.e. data frame versus vector) – ladylala Apr 07 '19 at 04:47

score 1 · Accepted Answer · answered Apr 07 '19 at 03:57

1

# A tibble: 2 x 2
  hello world
  <dbl> <dbl>
1     5     6
2     5     7
> col = 'hello'
> A[[col]]
[1] 5 5

answered Apr 07 '19 at 03:57

liuminzhao

2 Answers2