Applying a function with two arguments using Lapply

Question

I have created a test function, called testFunc which expects two arguments.

testFunc<-function(x,y){
  length(x)
  nrow(y)
}

Now I want to use lappy to apply this function to a list, keeping the y argument fixed.

Consider a test list, testList:

testList<-list(a=c(1,2,3,4,5,5,6),b=c(1,2,4,5,6,7,8))

Can we use lapply to run testFunc on testList$a and testList$b with same value of y?

I tried this call:

lapply(X = testList, FUN = testFunc, someDataFrame)

But I am always getting the length of someDataFrame as the output. Am I missing something obvious.

Why don't you set your y to be fixed within the function and use only x as argument? i.e. testfunc <- function(x, y=...) {...} ? — Sotos
– Sotos, Commented May 12, 2016 at 12:06
@Sotos : The code as it is posted already does the job. But, I think Tushar wants to return length(x) and nrow(y) both — vasanthcullen
– vasanthcullen, Commented May 12, 2016 at 12:17
@vasanthcullen I am expecting it to print the values 7, nrow(someDataFrame) two times, since testList has two vectors. All it gives me is 7 and nrow(someDataFrame) once. — tushaR
– tushaR, Commented May 12, 2016 at 13:08
@vasanthcullen Yeah, got it. I should have used print, to print the number of rows. I think the point you made regarding R printing the last evaluated value was the reason. Thanks. — tushaR
– tushaR, Commented May 12, 2016 at 13:16

vasanthcullen · Accepted Answer · 2016-05-12 12:05:50Z

1

Change your function to

testFunc<-function(x,y){
  return(c(length(x), nrow(y)))
}

By default, a R function returns the last evaluated value

answered May 12, 2016 at 12:05

vasanthcullen

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Comments

asb · Accepted Answer · 2016-05-12 12:06:24Z

1

Simplest way, use a named variable:

lapply(X = testList, FUN=testFunc, y=someDataFrame)

answered May 12, 2016 at 12:06

asb

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