Selecting multiple elements with [

df[rows, cols] selecting just one column:

• with a tibble you still get a data frame (tibble)
• but with a data.frame simplification to vector is applied:
  • except df[rows, cols, drop = FALSE]: maintains the data.frame class

df

##   x y     z
## 1 1 k FALSE
## 2 2 l  TRUE

df[, "z"]

## [1] FALSE  TRUE

df[, "z", drop = FALSE]

##       z
## 1 FALSE
## 2  TRUE