[R] Removing Zeros from matrix

[Dimitris Rizopoulos]

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)


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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>>
>
>

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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