[R] matrix subsetting

[Duncan Murdoch]

On 12-02-13 5:46 PM, R. Michael Weylandt <michael.weylandt at gmail.com> wrote:
> which(x>0)
>
> or
>
> which(x>0, arr.ind=TRUE)
>
> depending on your application.

Or even x>0 if you want a matrix of TRUE/FALSE values.  You can use 
x[x>0] to get the values, but they won't be in matrix form.

Duncan Murdoch


>
> Michael
>
> On Feb 13, 2012, at 5:38 PM, Sam Steingold<sds at gnu.org>  wrote:
>
>> if I have a vector, I can find the indexes which satisfy a condition:
>> x<- rnorm(10)
>> [1]  0.4751132 -0.5442322 -0.1979854 -0.2455521  0.8349336 -0.4283345
>> [7]  0.6108130  2.0576160  1.1251716 -1.3933637
>> x[x>0]
>> [1] 0.4751132 0.8349336 0.6108130 2.0576160 1.1251716
>> (1:10)[x>0]
>> [1] 1 5 7 8 9
>>
>> how about a matrix?
>>
>>        00000G      00000Q      00002O       000035       000037       00003A
>> 00000G     NA 0.008226002 0.005631718 0.0002625585 0.0010673235 0.0045310915
>> 00000Q     NA          NA 0.003714951 0.0002007877 0.0016983426 0.0011083925
>> 00002O     NA          NA          NA 0.0024233691 0.0069849678 0.0024510792
>> 000035     NA          NA          NA           NA 0.0006499707 0.0008420414
>> 000037     NA          NA          NA           NA           NA 0.0005448872
>> 00003A     NA          NA          NA           NA           NA           NA
>> 00003B     NA          NA          NA           NA           NA           NA
>> 00003G     NA          NA          NA           NA           NA           NA
>> 00003H     NA          NA          NA           NA           NA           NA
>> 00003I     NA          NA          NA           NA           NA           NA
>>              00003B       00003G       00003H      00003I
>> 00000G 0.0007254316 0.0093954826 3.420231e-04 0.003974556
>> 00000Q 0.0013883606 0.0019778247 3.609791e-05 0.001552725
>> 00002O 0.0027340806 0.0082790646 2.561862e-03 0.012297821
>> 000035 0.0006025767 0.0004534397 1.053946e-03 0.001681780
>> 000037 0.0005501974 0.0021137871 1.733880e-03 0.003712675
>> 00003A 0.0008969849 0.0043855527 2.786194e-06 0.002492954
>> 00003B           NA 0.0019791290 8.301787e-04 0.002816774
>> 00003G           NA           NA 3.181892e-07 0.010608717
>> 00003H           NA           NA           NA 0.001066141
>> 00003I           NA           NA           NA          NA
>>
>> how do I find the cells whose values are, e.g.,>  0.01 ??