R help - Sep 1999 - Re: [S] Putting values into matrices: desired behaviour?

>>>>> On Wed, 01 Sep 1999 08:34, Mette Langaas <Mette.Langaas
at nr.no> said:
    Mette> I'm running S-Plus 5.1 on UNIX (but the same behaviour I'm
    Mette> describing is seen on S-Plus 3.4 R1 for UNIX).

    Mette> I have first created a matrix with two rows and three columns

    >> test_matrix(ncol=3,nrow=2)
    >> test
    Mette>       [,1] [,2] [,3] 
    Mette> [1,]   NA   NA   NA
    Mette> [2,]   NA   NA   NA

    Mette> I then want to put values into parts of the matrix, but by mistake
I
    Mette> index outside the matrix (use rows 3-7 when there are only 2
rows).

    >> ind_matrix(c(1,2,3,4,5,6,7,2,2,2,2,2,2,2),ncol=2)
    >> ind
    Mette>      [,1] [,2] 
    Mette> [1,]    1    2
    Mette> [2,]    2    2
    Mette> [3,]    3    2
    Mette> [4,]    4    2
    Mette> [5,]    5    2
    Mette> [6,]    6    2
    Mette> [7,]    7    2
    >> test[ind]_c(3,4,5,6,7,8,9)
    >> test
    Mette>       [,1] [,2] [,3] 
    Mette> [1,]   NA    3    5
    Mette> [2,]   NA    4    6

    Mette> The first observation is that in addition to correctly putting
    Mette> values 3 ang 4 into position (1,2) and (2,2) the value 5 is put
    Mette> into (1,3) instead of (3,2) as requested and
    Mette> 6 is put into (2,3) instead of (4,3) as requested.

	   <...snip...>

    Mette> Is this the desired behaviour of indexing matrices? What
    Mette> measures can I take to avoid this behaviour -- e.g. to instead
    Mette> get an error message?

In R, you do get an error message
    ``Error: subscript out of bounds''
and  test[,] remains unaltered.

I hope nobody complains about non-compatibility with S...  ;-)

Martin Maechler <maechler at stat.math.ethz.ch>
http://stat.ethz.ch/~maechler/
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