[R] removeing only rows/columns with "na" value from square ( symmetrical ) matrix.

[Gabor Grothendieck]

On Sun, May 20, 2012 at 10:52 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> On Sun, May 20, 2012 at 10:17 AM, Nevil Amos <nevil.amos at monash.edu> wrote:
>> I have some square matrices with na values in corresponding rows and
>> columns.
>>
>> M<-matrix(1:2,10,10)
>> M[6,1:2]<-NA
>> M[10,9]<-NA
>> M<-as.matrix(as.dist(M))
>> print (M)
>>
>>    1 2 3 4 5 6 7 8 9 10
>> 1   0  2 1 2 1 NA 1 2  1  2
>> 2   2  0 1 2 1 NA 1 2  1  2
>> 3   1  1 0 2 1  2 1 2  1  2
>> 4   2  2 2 0 1  2 1 2  1  2
>> 5   1  1 1 1 0  2 1 2  1  2
>> 6  NA NA 2 2 2  0 1 2  1  2
>> 7   1  1 1 1 1  1 0 2  1  2
>> 8   2  2 2 2 2  2 2 0  1  2
>> 9   1  1 1 1 1  1 1 1  0 NA
>> 10  2  2 2 2 2  2 2 2 NA  0
>>
>>
>> How do I remove just the row/column pair( in this trivial example row 6 and
>> 10 and column 6 and 10) containing the NA values?
>>
>> so that I end up with all rows/ columns that are not NA - e.g.
>>
>>  1 2 3 4 5 7 8 9
>> 1 0 2 1 2 1 1 2 1
>> 2 2 0 1 2 1 1 2 1
>> 3 1 1 0 2 1 1 2 1
>> 4 2 2 2 0 1 1 2 1
>> 5 1 1 1 1 0 1 2 1
>> 7 1 1 1 1 1 0 2 1
>> 8 2 2 2 2 2 2 0 1
>> 9 1 1 1 1 1 1 1 0
>>
>
> Try this:
>
> ix <- na.action(na.omit(replace(M, upper.tri(M), 0)))
> M[-ix, -ix]

and here is a minor variation which is slightly shorter:

ix <- complete.cases(replace(M, upper.tri(M), 0))
M[ix, ix]

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