[R] how to skip a specific value when using apply() function to a matrix?

[Shuhua Zhan]

Hello Nikhil and Wu,
Thank you very much for your reply!
What I want is to calculate the student's score column-wise by ignoring the specific values such as zeros for example only using c(2,1) in column 8 in the tmp1 and generate tmp2. I changed the zeros to NAs and modified my stud fun to student as below. So I can ignore these specific values but can not put back the NAs to the right position in the resulted matrix.
Any suggestions to put back NAs to their original positions in column 7 and 8 either to list tmp4 or matrix tmp5?

tmp1[tmp1==0]<-NA
student<- function(x){
    x<-x[!is.na(x)]
    x<-(x-mean(x))/sd(x)
    return (x)
}
tmp4<-apply(tmp1, 2, student)
tmp4
[[1]]
[1]  1.1296201  0.1613743 -1.2909944  1.1296201 -0.3227486 -0.8068715

[[2]]
[1]  0.0000000  0.0000000 -1.4680505 -0.5872202  0.5872202  1.4680505

[[3]]
[1] -0.5207910 -0.4817316 -0.4036130  0.2994548  1.9008870 -0.7942062

[[4]]
[1] -0.8630035 -0.2380699 -0.7737273 -0.5951748  1.5474546  0.9225210

[[5]]
[1] -0.1913482 -0.6944435 -0.7202433  0.5826446  1.7565336 -0.7331431

[[6]]
[1] -0.1132277  0.5661385 -1.4719601 -0.7925939  0.5661385  1.2455047

[[7]]
[1] -0.9561829  0.2390457  1.4342743  0.2390457 -0.9561829

[[8]]
[1]  0.7071068 -0.7071068

tmp5<- matrix(unlist(tmp4),nrow=6)
tmp5
           [,1]       [,2]       [,3]       [,4]       [,5]       [,6]       [,7]       [,8]
[1,]  1.1296201  0.0000000 -0.5207910 -0.8630035 -0.1913482 -0.1132277 -0.9561829 -0.7071068
[2,]  0.1613743  0.0000000 -0.4817316 -0.2380699 -0.6944435  0.5661385  0.2390457  1.1296201
[3,] -1.2909944 -1.4680505 -0.4036130 -0.7737273 -0.7202433 -1.4719601  1.4342743  0.1613743
[4,]  1.1296201 -0.5872202  0.2994548 -0.5951748  0.5826446 -0.7925939  0.2390457 -1.2909944
[5,] -0.3227486  0.5872202  1.9008870  1.5474546  1.7565336  0.5661385 -0.9561829  1.1296201
[6,] -0.8068715  1.4680505 -0.7942062  0.9225210 -0.7331431  1.2455047  0.7071068 -0.3227486

Joshua

----- Original Message -----
From: "Shuhua Zhan" <szhan at uoguelph.ca>
To: r-help at r-project.org
Sent: Thursday, July 15, 2010 11:08:34 PM GMT -05:00 US/Canada Eastern
Subject: [R] how to skip a specific value when using apply() function to a matrix?

Hello R experts,
I'd like to studentize a matrix (tmp1) by column using apply() function and skip some specific values such as zeros in the example below to tmp2 but not tmp3. I used the script below and only can get a matrix tmp3. Could you please help me to studentize the matrix (tmp1) without changing the zeros and generate a new matrix tmp2?
Thanks,
Joshua

tmp1
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
[1,]   15    7    9   49   60    3    2    0
[2,]   13    7   10   56   21    4    3    0
[3,]   10    2   12   50   19    1    0    2
[4,]   15    5   30   52  120    2    4    0
[5,]   12    9   71   76  211    4    3    1
[6,]   11   12    2   69   18    5    2    0

tmp2
[1,]  1.1296201  0.0000000 -0.5207910 -0.8630035 -0.1913482 -0.1132277 -0.9561829  0.0000000
[2,]  0.1613743  0.0000000 -0.4817316 -0.2380699 -0.6944435  0.5661385  0.2390457  0.0000000
[3,] -1.2909944 -1.4680505 -0.4036130 -0.7737273 -0.7202433 -1.4719601  0.0000000  0.7071068
[4,]  1.1296201 -0.5872202  0.2994548 -0.5951748  0.5826446 -0.7925939  1.4342743  0.0000000
[5,] -0.3227486  0.5872202  1.9008870  1.5474546  1.7565336  0.5661385  0.2390457 -0.7071068
[6,] -0.8068715  1.4680505 -0.7942062  0.9225210 -0.7331431  1.2455047 -0.9561829  0.0000000

tmp3
          [,1]       [,2]       [,3]       [,4]       [,5]       [,6]      [,7]       [,8]
[1,]  1.1296201  0.0000000 -0.5207910 -0.8630035 -0.1913482 -0.1132277 -0.243975 -0.5976143
[2,]  0.1613743  0.0000000 -0.4817316 -0.2380699 -0.6944435  0.5661385  0.487950 -0.5976143
[3,] -1.2909944 -1.4680505 -0.4036130 -0.7737273 -0.7202433 -1.4719601 -1.707825  1.7928429
[4,]  1.1296201 -0.5872202  0.2994548 -0.5951748  0.5826446 -0.7925939  1.219875 -0.5976143
[5,] -0.3227486  0.5872202  1.9008870  1.5474546  1.7565336  0.5661385  0.487950  0.5976143
[6,] -0.8068715  1.4680505 -0.7942062  0.9225210 -0.7331431  1.2455047 -0.243975 -0.5976143

Here is my script:
stud<- function(x){
    x<-(x-mean(x))/sd(x)
    return (x)
}
tmp3<-apply(tmp1,2,stud)

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