R tip iterating over list

To iterate over a list by key, value pair, do this:

for (name in names(myList)) {
    print(name)

    print(myList[[name]])

}

Note the double [[]] so you get just the value, not the pair.

This entry was posted on Tuesday, March 16th, 2010 at 10:52 pm and is filed under feature, r, stats. You can follow any comments to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

9 comments

  1. Ian Lewis
    January 11, 2011 at 10:45 am

    Thanks for that snippet!

    I was able to write a script that allows me to list the levels associated with each of the named variables.

    Ian

  2. Matt
    October 27, 2011 at 4:37 pm

    Very helpful. Better than the usual “LOOPS ARE EVIL!!111111” instructions. Thanks!

  3. David Beckwith
    March 3, 2014 at 10:07 am

    The formatting of your code snippet is showing tags.

  4. Anthony Boyles
    April 14, 2014 at 12:41 pm

    Hey man,
    I know this post is pretty old, but I just wanted to say “Thanks.” It just helped me shorten a chunk of code from hundreds of lines down to ten.
    Tony

  5. NBA
    June 26, 2015 at 3:43 pm

    Thanks! so useful.

  6. prashan
    August 15, 2015 at 6:12 pm

    Thanks!…simple and effective …I m transitioning from python

  7. etgriffonage
    October 16, 2016 at 5:55 pm

    This legit just solved a problem I was having all weekend. THANKS!

  8. Ashraf
    September 25, 2017 at 6:12 am

    Thanks for the tip on iterating over a list. I have the following function to iterate over a list, which is a river network formed by various segments, but the result is always one segment, I’m missing something in the code, any suggestions?

    my code:
    test.func = function(x){
    for (i in 1:length(x)) {
    tt[[i]] <- x[i]; tt[[i]] = Line(tt[[i]]); tt[[i]] = Lines(list(tt[[i]] ), 'i')
    tt1 = SpatialLines(list(tt[[i]]))
    }
    return(tt1)
    }

  9. Oliver
    November 9, 2017 at 6:49 am

    Helped me too, thank you!