Slightly more sane head() for lists in R

head.list.R

catDf <- data.frame(meow = rnorm(100), purr = rpois(100, 3))
aList <- list(aVector = 1:20, aDf = catDf, anotherList = list(1:200, 1:20))

# annoying as hell, right?
head(aList)

#' Return the first or last part of a list
#'
#' Returns the first or last part of a list. Instead of returning the first
#' n entries as the standard head() does, it attempts to call head()
#' recursively on the entries in the list. If it fails, it will return the
#' particular entry (standard behavior).
#' @param obj a list object
#' @param n a single integer. If positive, prints the first n items for the
#' list and all entries in the list. If negative, prints all but the last
#' n items in the list.
#' @return a list of length n, with items in the list of length n
head.list <- function(obj, n = 6L, ...)
{
    stopifnot(length(n) == 1L)
    origN <- n
    n <- if (n < 0L)
        max(length(obj) + n, 0L)
    else min(n, length(obj))
    lapply(obj[seq_len(n)], function(x)
           {
               tryCatch({
                   head(x, origN, ...)
               }, error = function(e) {
                   x
               })
           })
}
environment(head.list) <- asNamespace('utils')

# less annoying behavior!
head(aList)

This is so awesome!

nice

Nice, thanks!

Thanks so much!

Awesome!