Question

I have a bunch of large dataframes, so every time I want to display them, I have to use head:

head( blahblah(somedata) )

Typing head all the time gets old after the first few hundred times, so I’d like an easy way to do this if possible. One of the cool things about R compared to java that things like this are often really easy, if you know the secret incantation.

I searched in options, and found max.print, which almost works, except there is now a time delay.

head( blahblah(somedata) )

…. is instantaneous (to within the limits of my perception)

options(max.print=100)
blahblah(somedata)

…. takes about 3 seconds, so longer than typing head

Is there some way of making head be applied automatically when printing large data structures?

An piece of code which reproduces this behavior:

long_dataset = data.frame(a = runif(10e5), 
                          b = runif(10e5), 
                          c = runif(10e5))
system.time(head(long_dataset))
options(max.print = 6)
system.time(print(long_dataset))

Answer 1

I’d go along with @thelatemail’s suggestion, i.e. redefine print.data.frame:

print.data.frame <- function(df) {
   if (nrow(df) > 10) {
      base::print.data.frame(head(df, 5))
      cat("----\n")
      base::print.data.frame(tail(df, 5))
   } else {
      base::print.data.frame(df)
   }
}

data.frame(x=1:100, y=1:100)
#   x y
# 1 1 1
# 2 2 2
# 3 3 3
# 4 4 4
# 5 5 5
# ----
#       x   y
# 96   96  96
# 97   97  97
# 98   98  98
# 99   99  99
# 100 100 100

A more elaborate version could line everything up together and avoid the repeated header, but you get the idea.

You could put such function in your .Rprofile or Rprofile.site files (see ?Startup) so it will be there every time you start an R session.