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logical condition in vector operation

4 messages · Federico Calboli, Christoph Buser, PIKAL Petr

Federico Calboli
# 
HI All,

I have a data frame such as:
x y  p  d
[1,] 1 0 10 21 0
[2,] 2 3 11 12 0
[3,] 3 4 12 23 0
[4,] 3 5 13 24 0


and I want to perfor some operations on the first two coulums,
conditional on the uneqaulity values on the 3rd and 4th columns.

For instance:

j = 3
test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]

gives me the result:

test:

     x y  p  d
[1,] 1 0 10 21 0
[2,] 2 3 11 12 0
[3,] 3 4 12 23 6
[4,] 3 5 13 24 7


My probblem is the following: I want to perform the operation
test[test[,1] == j,2] + test[test[,2] == j,1] only if the value of
column p and column d are different at the positions where x or y = j.
In practice, I don't want to perform the first operation because
test[2,4 is 12 and test[1,3] is 12 as well.

I tried an if statement with little success:

if(test[test[,1] == j,3] != test[test[,2] == j,4]){
test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]
}
Warning message:
the condition has length > 1 and only the first element will be used in:
if (test[test[, 1] == j, 3] != test[test[, 2] == j, 4]) {

Could anyone lend some advice?

Cheers,

Federico
Christoph Buser
# 
Dear Frederico
Please have a look on the slightly changed example here (I
changed two values to show a potentially undesired side effect of
your coding.


test <- data.frame(rbind(c(3,3,10,21,0), c(2,3,11,12,0), c(3,4,12,23,0),
                         c(3,5,13,24,0)))
names(test) <- c("x","y","p","d","su")
test
j <- 3
test[test[,1] == j, 5] <- test[test[,1] == j,2] + test[test[,2] == j,1]
Your code example produces now a warning for the adapted
data frame "test", since one tries to add two vectors of length 2
and 3, respectively. The result is based on recycling of the
smaller vector. In your example there was no warning since the
second column had only one entry.
The result with the adapted data frame is:

test
Is that kind of recycling desired in your application. Otherwise
you should be careful with the coding example above.

Regards,

Christoph Buser

--------------------------------------------------------------
Christoph Buser <buser at stat.math.ethz.ch>
Seminar fuer Statistik, LEO C13
ETH (Federal Inst. Technology)	8092 Zurich	 SWITZERLAND
phone: x-41-44-632-4673		fax: 632-1228
http://stat.ethz.ch/~buser/
--------------------------------------------------------------






Federico Calboli writes:
 > HI All,
 > 
 > I have a data frame such as:
 > 
 > > test
 >      x y  p  d
 > [1,] 1 0 10 21 0
 > [2,] 2 3 11 12 0
 > [3,] 3 4 12 23 0
 > [4,] 3 5 13 24 0
 > 
 > 
 > and I want to perfor some operations on the first two coulums,
 > conditional on the uneqaulity values on the 3rd and 4th columns.
 > 
 > For instance:
 > 
 > j = 3
 > test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]
 > 
 > gives me the result:
 > 
 > test:
 > 
 >      x y  p  d
 > [1,] 1 0 10 21 0
 > [2,] 2 3 11 12 0
 > [3,] 3 4 12 23 6
 > [4,] 3 5 13 24 7
 > 
 > 
 > My probblem is the following: I want to perform the operation
 > test[test[,1] == j,2] + test[test[,2] == j,1] only if the value of
 > column p and column d are different at the positions where x or y = j.
 > In practice, I don't want to perform the first operation because
 > test[2,4 is 12 and test[1,3] is 12 as well.
 > 
 > I tried an if statement with little success:
 > 
 > if(test[test[,1] == j,3] != test[test[,2] == j,4]){
 > test[test[,1] == j, 5] = test[test[,1] == j,2] + test[test[,2] == j,1]
 > }
 > Warning message:
 > the condition has length > 1 and only the first element will be used in:
 > if (test[test[, 1] == j, 3] != test[test[, 2] == j, 4]) {
 > 
 > Could anyone lend some advice?
 > 
 > Cheers,
 > 
 > Federico
 > -- 
 > Federico C. F. Calboli
 > Department of Epidemiology and Public Health
 > Imperial College, St Mary's Campus
 > Norfolk Place, London W2 1PG
 > 
 > Tel  +44 (0)20 7594 1602     Fax (+44) 020 7594 3193
 > 
 > f.calboli [.a.t] imperial.ac.uk
 > f.calboli [.a.t] gmail.com
 > 
 > ______________________________________________
 > 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
Federico Calboli
#
On Thu, 2006-02-09 at 09:22 +0100, Christoph Buser wrote:
Recycling was and is integral part of my plan.

Cheers,

Federico
PIKAL Petr
# 
Hi

try
ifelse()

but I you probably shall put your problem clearer.

HTH
Petr
On 8 Feb 2006 at 18:12, Federico Calboli wrote:
From:           	Federico Calboli <f.calboli at imperial.ac.uk>
To:             	r-help <r-help at stat.math.ethz.ch>
Organization:   	Imperial College London
Date sent:      	Wed, 08 Feb 2006 18:12:37 +0000
Subject:        	[R] logical condition in vector operation
Send reply to:  	f.calboli at imperial.ac.uk
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Petr Pikal
petr.pikal at precheza.cz