R data frame columns from vector

Question

I must be missing something obvious here but for this:

> range(data$timestamp)
[1] "2015-06-29 09:32:43.000 UTC" "2015-07-03 15:50:35.986 UTC"

I want to do something like:

df <- data.frame(as.Date(range(data$timestamp)))
names(df) <- c('from', 'to')

and get a data frame with columns 'from' and 'to' without needing an extra variable only to index. Written as above data.frame converts the vector to two rows in a single-column data frame. I've tried various combinations of cbind, matrix, t, list and attempts at destructuring. What is the best way to do this?

Answer 1

df <- as.data.frame(as.list(as.Date(range(data$timestamp))))
names(df) <- c('from', 'to')

This will work. data.frames are really just special lists after all.

If you wanted a one-liner, you could use setNames. I've also found this type of thing much more readable now using magrittr:

data$timestamp %>% range %>% as.Date %>% as.list %>% as.data.frame %>% setNames(c("from", "to")

Alternatively, you could cast via a matrix:

df <- as.data.frame(matrix(as.Date(range(data$timestamp)), ncol = 2))
names(df) <- c('from', 'to')

This will, however, strip the class (and other attributes) from the dates. If you instead set the dimensions of the vector using dim<-, then neither print nor as.data.frame will treat it as a matrix (because it still has the class Date).

To get round this, convert to Date after creating the data.frame:

df <- as.data.frame(matrix(range(data$timestamp), ncol = 2))
df[] <- lapply(df, as.Date)
names(df) <- c('from', 'to')