[R] Apply a function to columns of a matrix

[arun]

Hi,
You can also use sapply()
sapply(split(t(a),1:ncol(a)),function(x) sum(diff(b)*(x[-1]+x[-length(x)]))/2)
#   1    2    3    4    5    6    7    8    9   10 
  #99  279  459  639  819  999 1179 1359 1539 1719 
A.K.



----- Original Message -----
From: Andras Farkas <motyocska at yahoo.com>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Saturday, September 8, 2012 3:45 PM
Subject: [R] Apply a function to columns of a matrix

Dear All,
 
as a follow up to my previous e-mail (I think I am getting closer...):
 
I am trying to apply the trapezoidal functions to a matric column by column. I have the following code:
 
a <-matrix(c(1:100),ncol=10)
b <-matrix(c(2,4,6,8,10,12,14,16,18,20))
 
apply(a,2,function(b,a) sum(diff(b)*(a[-1]+a[-length(a)]))/2)
 
for some reason i get an error message:
Error in FUN(newX[[, i], ...): argument "a" is missing with no default.
 
Any ideas of why that may be happening?
 
thanks,
 
Andras
    [[alternative HTML version deleted]]


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