[R] Removing Zeros from matrix

[Paul Hiemstra]

Dimitris Rizopoulos wrote:
>
>
> On 3/9/2010 1:36 PM, Paul Hiemstra wrote:
>> Dimitris Rizopoulos wrote:
>>> one approach is the following:
>>>
>>> mat <- matrix(rnorm(100*45), 100, 45)
>>> mat[sample(100*45, 50)] <- 0
>>>
>>> index <- rowMeans(mat == 0) == 0
>>> mat[index, ]
>> Dimitris,
>>
>> You use quite a complicated syntax to get the index. I think the
>> following syntax using apply is more easy to understand:
>
> well, this way is much more efficient to compute, especially if you 
> have many rows. Compare the following to see the difference:
>
> mat <- matrix(rnorm(2*1e06), 1e06, 2)
> mat[sample(2*1e06, 50)] <- 0
>
> system.time(index1 <- !apply(mat == 0, MARGIN = 1, any))
>
> system.time(index2 <- rowMeans(mat == 0) == 0 )
>
> all.equal(index1, index2)
Point taken, I totally agree that for large matrices you should use your 
approach. Didn't know that it made such a difference, great to learn 
something new :). But I still like the other syntax more ;).

cheers,
Paul
>
>
> Best,
> Dimitris
>
>
>> # Note, MARGIN equal to 1 means loop over rows
>> # If any member of a row is zero
>> index = apply(mat == 0, MARGIN = 1, any)
>> # If all members of a row are zero
>> index = apply(mat == 0, MARGIN = 1, all)
>>
>> cheers and hope it helps,
>> Paul
>>>
>>>
>>> I hope it helps.
>>>
>>> Best,
>>> Dimitris
>>>
>>>
>>> On 3/9/2010 11:05 AM, ogbos okike wrote:
>>>> Hi Everybody,
>>>> I have a matrix of about 45 columns. Some of the rows contain zeros.
>>>> Using
>>>>> data1<-data[complete.cases(data),], I can remove the "NA" rows. But
>>>>> I am
>>>> unable to tackle that of zeros.
>>>> Can anybody give me an idea of how to remove rows containing zeros 
>>>> in a
>>>> matrix.
>>>> Thanks so much
>>>> Best
>>>> Ogbos
>>>>
>>>> [[alternative HTML version deleted]]
>>>>
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>>>
>>
>>
>


-- 
Drs. Paul Hiemstra
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