CODEWITHSUNDEEP
rtidyverse
sieste
sieste

Reputation: 9017

Print first few lines of a text file in R

I have a text file with no apparent tabular or other structure, for example with contents

some text on line 1
some more text on line 2
even more text on the third line
etc

What is the most elegant and R-like way to print out the first few (say 2) lines of text from this file to the console?

Option 1: readLines

readLines('file.txt', n=2)
# [1] "some text on line 1"      "some more text on line 2"

The n=2 option is useful, but I want the raw file contents, not the individual lines as elements of a vector.

Option 2: file.show

file.show('file.txt')
# some text on line 1
# some more text on line 2
# even more text on the third line
# etc

This output format is what I would like to see, but an option to limit the number of lines, like n=2 in readLines, is missing.

Option 3: system('head')

system('head -n2 file.txt')
# some text on line 1
# some more text on line 2

That's exactly the output I would like to get, but I'm not sure if this works on all platforms, and invoking an external command for such a simple task is a bit awkward.

One could combine the readLines solution with paste and cat to format the output, but this seems excessive. A simple command like file.head would be nice, or a n=2 argument in file.show, but neither exists. What is the most elegant and compact way to achieve this in R?

To clarify the goal here: This is for a write up of an R tutorial, where the narrative is something like "... we now have written our data to a new text file, so let's see if it worked by looking at the first couple of lines ...". At this point a simple and compact R expression, using base (update: or tidyverse) functions, to do exactly this would be very useful.

Upvotes: 5

Views: 6451

Answers (1)

G. Grothendieck
G. Grothendieck

Reputation: 269481

Use writeLines with readLines:

writeLines(readLines("file.txt", 2))

giving:

some text on line 1
some more text on line 2

This could alternately be written as the following pipeline. It gives the same output:

library(magrittr)

"file.txt" %>% readLines(2) %>% writeLines

Upvotes: 8

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