[R] looping through columns in a matrix or data frame

[arun]

Hi,
May be this helps:

Using your function:
mapply(less,test,4)

#or
 invisible(mapply(less,test,4))
#[1] 2 3
#[1] 3

#or

 for(i in 1:ncol(test)){
 less(test[,i],4)}
#[1] 2 3
#[1] 3


A.K.



Hi, I'm trying to figure out how to loop through columns in a matrix or 
data frame, but what I've been finding online has not been very clear. 
I've written the following simple function that I can use on a column to extract all values that are less than a specified number. Consider the 
following example using that function to extract all values less than 4 
from column1 of the table "test" 

> less <- function(x,y){print(x[which(x < y)])} 

> test 
  column1 column2 
1       2       3 
2       3       4 
3       4       5 

> less(test[,1],4) 
[1] 2 3 


What I want to do is loop that function over all the columns
 in the table. Note: I realize that this is a silly example and there 
are better ways to do this particular function in R, so please don't 
respond with better ways to extract values less than a given number. The
 question that I am interested in is merely how do I loop over the 
columns. If you could respond by modifying my silly function so that it 
will loop, that would be the most helpful response. Thanks for the 
advice!