Hi,
I try to make a simple for loop with a if else statement (First example - Below)
and extend it to a more complex loop (Second example). However, my results
#First example:
x=c(1,2)
t=for(i in 1:length(x)){
if (x==1){a=x+1}else
if (x==2){a=x}
}
Returned from R:
Warning messages:
1: the condition has length > 1 and only the first element will be used in:
if (x == 1) {
2: the condition has length > 1 and only the first element will be used in:
if (x == 1) {> t
[1] 2 3
However, the result i had liked to get was t=c(2,2) i.e. using the first
function (a=x+1) for x[1] and (a=x) for x[2]. I can remove the Warnings by
making: if (x[i]==1) etc. but this do not make the results any better.
#Second example:
x=c(1,2)
t<-for(i in 1:length(x)){
if (x==1){
a=x
b=x-1}else
if (x==2){
a=x+1
b=x}
b<-list(a=a,b=b)
}
Returned from R:
Warning messages:
1: the condition has length > 1 and only the first element will be used in:
if (x == 1) {
2: the condition has length > 1 and only the first element will be used in:
if (x == 1) {> t
$a
[1] 1 2
$b
[1] 0 1
The result i like to get are $a =c(1,3) and $b=c(0,2)
Probably there are couple of things that I do wrong and I appreciate all help!
On 9/4/2007 9:59 AM, Hans Ole ?rka wrote:> Hi, > I try to make a simple for loop with a if else statement (First example - Below) and extend it to a more complex loop (Second example). However, my results > > #First example: > x=c(1,2) > t=for(i in 1:length(x)){ > if (x==1){a=x+1}else > if (x==2){a=x} > } > > Returned from R: > Warning messages: > 1: the condition has length > 1 and only the first element will be used in: if (x == 1) { > 2: the condition has length > 1 and only the first element will be used in: if (x == 1) { >> t > [1] 2 3 > > However, the result i had liked to get was t=c(2,2) i.e. using the first function (a=x+1) for x[1] and (a=x) for x[2]. I can remove the Warnings by making: if (x[i]==1) etc. but this do not make the results any better.x is a vector of length 2. Using a = x + 1 means that the entire vector a will be replaced by the entire vector x. You need to index each entry each time you use it, i.e. if (x[i] == 1) a[i] <- x[i] + 1 else if (x[i] ==2]) a[i] <- x[i] or more simply, throw away the loop, and use the ifelse function: a <- ifelse( x == 1, x + 1, ifelse( x == 2, x, NA) ) (where I've used NA for the case where x is neither 1 nor 2.) Duncan Murdoch> > #Second example: > x=c(1,2) > t<-for(i in 1:length(x)){ > if (x==1){ > a=x > b=x-1}else > if (x==2){ > a=x+1 > b=x} > b<-list(a=a,b=b) > } > > Returned from R: > Warning messages: > 1: the condition has length > 1 and only the first element will be used in: if (x == 1) { > 2: the condition has length > 1 and only the first element will be used in: if (x == 1) { >> t > $a > [1] 1 2 > > $b > [1] 0 1 > > The result i like to get are $a =c(1,3) and $b=c(0,2) > > Probably there are couple of things that I do wrong and I appreciate all help! > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.
Hans,
I think your problem is that you don't use the variable which takes
different values in your if statement .... your "i" changes values and
has really nothing to do with your x variable (except the length part ....).
Also all the other variables need to be declared somehow - otherwise how can you
store values in them???
So your first code may be something like that:
t=c(1,2)
for(i in 1:length(t)){
if (i==1) t[i]=i+1 else t[i]=i
}
t[1] 2 2
and your second code:
a = c(1,2)
b=c(1,2)for(i in 1:2){if (i==1){a[i]=ib[i]=i-1} else{
a[i]=i+1b[i]=i}c<-list(a=a,b=b)}> c$a[1] 1 3> c$b[1] 0 2
Also when you have only 2 possible values for "i" i don't think
the second "if" is necessary. I hope this helps a little, although my
explanation is not necessarily the best.
Monica
------------------------------ Message: 16Date: Tue, 4 Sep 2007 15:59:54
+0200From: Hans Ole ?rka <hans-ole.orka@umb.no>Subject: [R] For loop with
if else statementTo: "'r-help@stat.math.ethz.ch'"
<r-help@stat.math.ethz.ch>Message-ID:<79A4337FAC9B9745AC67F907304190C0106A7226E5@exch01.ans.umb.no>Content-Type:
text/plain; charset="iso-8859-1" Hi,I try to make a simple for loop
with a if else statement (First example - Below) and extend it to a more complex
loop (Second example). However, my results #First example:x=c(1,2)t=for(i in
1:length(x)){if (x==1){a=x+1}elseif (x==2){a=x}} Returned from R:Warning
messages:1: the condition has length > 1 and only the first element will be
used in: if (x == 1) {2: the condition has length > 1 and only the first
element will be used in: if (x == 1) {> t[1] 2 3 However, the result i had
liked to get was t=c(2,2) i.e. using the first function (a=x+1) for x[1] and
(a=x) for x[2]. I can remove the Warnings by making: if (x[i]==1) etc. but this
do not make the results any better. #Second example:x=c(1,2)t<-for(i in
1:length(x)){if (x==1){a=xb=x-1}elseif (x==2){a=x+1b=x}b<-list(a=a,b=b)}
Returned from R:Warning messages:1: the condition has length > 1 and only the
first element will be used in: if (x == 1) {2: the condition has length > 1
and only the first element will be used in: if (x == 1) {> t$a[1] 1 2 $b[1] 0
1 The result i like to get are $a =c(1,3) and $b=c(0,2) Probably there are
couple of things that I do wrong and I appreciate all help!
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