R：用paste（）定义列名

Question

The question is pretty simple but I couldn't find a solution.

I want to create a new dataframe defining the name of the column with paste0 .

Ideally I would like to do something like this (which of doesn't work).

mydataframe <- data.frame(id = 1,
                          paste0('Here_','my_','column_','name') = 'foo')
# Error: unexpected '=' in:
#   "mydataframe <- data.frame(id = 1,
#                           paste0('Here_','my_','column_','name') ="

Also, why doesn't work?

Answer 1

Data.frame is a function, and therefore takes arguments. These arguments cannot be other functions. For example, you could not define a function like fn <- function(paste0('Hi_', 'how_are_you') = x) { x } . R just doesn't work that way.

However, you still can dynamically change your column names after the fact:

df <- data.frame(1, 'foo')
names(df) <- c('id', paste0('Here_','my_','column_','name'))

That should do what you want.

Bonus: You can simplify your paste as follows: paste('Here', 'my', 'column', 'name', sep = '_') .

Answer 2

You can do

df[, paste('Here', 'my', 'column', 'name', sep = '_')] <- 'foo'

It is impossible to do it as you suggest, because no variable is evaluated, it just gets exactly what you are writing and trying to use it as a name for the column. This way, paste('Here', 'my', 'column', 'name', sep = '_') gets evaluated and the returned string is actually used as a name for the column.

Answer 3

I needed the same some time ago and solved the problem with putting all the command inside paste function with following evaluation

i=3
mydf <- eval(parse(text = paste0(
  "data.frame( id =", 1, ", my_col", i, "=", 55, ")")))