r - Are dataframe[ ,-1] and dataframe[-1] the same?

Question

Sorry this seems like a really silly question but are dataframe[ ,-1] and dataframe[-1] the same, and does it work for all data types?

And why are they the same

Answer 1

Almost.

[-1] uses the fact that a data.frame is a list, so when you do dataframe[-1] it returns another data.frame (list) without the first element (i.e. column).

[ ,-1]uses the fact that a data.frame is a two dimensional array, so when you do dataframe[, -1] you get the sub-array that does not include the first column.

A priori, they sound like the same, but the second case also tries by default to reduce the dimension of the subarray it returns. So depending on the dimensions of your dataframe you may get a data.frame or a vector, see for example:

> data <- data.frame(a = 1:2, b = 3:4)
> class(data[-1])
[1] "data.frame"
> class(data[, -1])
[1] "integer"

You can use drop = FALSE to override that behavior:

> class(data[, -1, drop = FALSE])
[1] "data.frame"