R: Subsetting a list based on a condition

Posted by markbulling ⋅ January 19, 2012 ⋅ 5 Comments

Quite a handy couple of lines of code to subset a list in R to just those elements which meet a certain condition. Here’s an example to return only those elements of a list which are a certain class.

Thanks to this StackOverflow answer.


list.condition <- sapply(input.list, function(x) class(x)=="desired.class")
output.list  <- input.list[list.condition]

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Discussion

5 Responses to “R: Subsetting a list based on a condition”

As I just posted to the StackOverflow thread, this is what the Filter() function was made for. Also, you may want to avoid using `==’ to test for an object’s class. Check out inherits() — much more robust.

Posted by Jason | January 20, 2012, 12:44 am

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- Thanks for this Jason. I hadn’t come across Filter() (or any other of the higher level functions) before, so will check them out.
  
  Posted by markbulling | January 23, 2012, 8:47 pm
  
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Another option is the subset() function.

Posted by Ken | January 26, 2012, 1:19 am

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- Hi Ken
  
  Does subset work with lists? From the documentation, it looks like it only works with vectors, matrices or data frames. Also, I’m trying to get more into the [] notation as I’m a big user of subset.
  
  Cheers
  
  Mark
  
  Posted by markbulling | January 26, 2012, 8:10 pm
  
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