[R] Logical function to turn missing values to 0's

[ONKELINX, Thierry]

Use the is.na function to test for NA values. And do read about
vectorizing your code. You don't need loops for this problem. Without
loops your code will run more than 400 times faster!

> n <- 1000
> x <- matrix(data=rep(c(1,2,3,NA), n), ncol=n, nrow=n)
> 
> system.time({
+     y <- matrix(data=0, ncol=ncol(x), nrow=nrow(x))
+     for(i in 1:nrow(x)) {
+         for(j in 1:ncol(x)) {
+             y[i,j] <- ifelse(is.na(x[i,j]), 0, x[i,j])
+     }
+     }
+ })
   user  system elapsed 
  45.17    0.30   45.61 
> system.time(y <- ifelse(is.na(x), 0, x))
   user  system elapsed 
   0.60    0.15    0.75 
> system.time({
+     y <- x
+     y[is.na(x)] <- 0
+ })
   user  system elapsed 
   0.11    0.00    0.11 


------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens rafamoral
Verzonden: woensdag 14 januari 2009 23:32
Aan: r-help at r-project.org
Onderwerp: [R] Logical function to turn missing values to 0's


I have a dataset which contains some missing values, and I need to
replace
them with zeros. I tried using the following:

x <- matrix(data=rep(c(1,2,3,NA),6), ncol=6, nrow=6)

y <- matrix(data=0, ncol=ncol(x), nrow=nrow(x))

for(i in 1:nrow(x)) {

for(j in 1:ncol(x)) {

y[i,j] <- ifelse(x[i,j]==NA, 0, x[i,j])

}}

But y returns an NA matrix.
I'd appreciate any help.
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