Alternating between "for loops"

Dear All,
I would like to apply two different "for loops" to each set of four columns
of a matrix (the loops here are simplifications of the actual loops I will
be running which involve multiple if/else statements).
I don't know how to "alternate" between the loops depending on which column
is "running through the loop" at the time.
## Set up matrix
J <- 10
N <- 10
y <- matrix(0,N,J)
## Apply this loop to the first two of every four columns ([,1:2],
[,5:6],[,9:10], etc.)
for (q in 1:N){
for(j in 1:J){
if(j %% 2){
y[q,j]=1
}else{y[q,j]=2}
}
}
## Apply this loop to the next two of every four columns
([,3:4],[,7:8],[,11:12], etc.)
for (q in 1:N){
for(j in 1:J){
if(j %% 2){
y[q,j]="A"
}else{y[q,j]="B"}
}
}
I want to get something like this (preferably without the quotes):

y

[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
  [1,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [2,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [3,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [4,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [5,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [6,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [7,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [8,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [9,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
[10,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"



Any help greatly appreciated!

Claudia

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Hello,

Maybe something along the lines of

J <- 10
cols <- rep(c(TRUE, TRUE, FALSE, FALSE), 3)[seq_len(J)]
for(i in which(cols)) { do something }
for(i in which(!cols)) { do something else }

Hope this helps,

Rui Barradas

Em 31-07-2012 00:18, Claudia Penaloza escreveu:

Dear All,
I would like to apply two different "for loops" to each set of four 
columns
of a matrix (the loops here are simplifications of the actual loops I 
will
be running which involve multiple if/else statements).
I don't know how to "alternate" between the loops depending on which 
column
is "running through the loop" at the time.
## Set up matrix
J <- 10
N <- 10
y <- matrix(0,N,J)
## Apply this loop to the first two of every four columns ([,1:2],
[,5:6],[,9:10], etc.)
for (q in 1:N){
for(j in 1:J){
if(j %% 2){
y[q,j]=1
}else{y[q,j]=2}
}
}
## Apply this loop to the next two of every four columns
([,3:4],[,7:8],[,11:12], etc.)
for (q in 1:N){
for(j in 1:J){
if(j %% 2){
y[q,j]="A"
}else{y[q,j]="B"}
}
}
I want to get something like this (preferably without the quotes):

y

[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
  [1,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [2,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [3,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [4,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [5,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [6,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [7,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [8,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
  [9,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"
[10,] "1"  "2"  "A"  "B"  "1"  "2"  "A"  "B"  "1"  "2"



Any help greatly appreciated!

Claudia

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