That's a good one, Using cumsum + rowsum would definitely be faster,
On Tue, May 21, 2013 at 6:40 AM, José Verhoeven <j...@memo2.nl> wrote:
> Thank you, that really worked. Actually received an even shorter version:
>
>
> rowSums((t(apply(D > 0, 1, cumsum)) <= 3) * D)
>
>
>
> 2013/5/21 Xiao He <praguewaterme...@gmail.com>
>
>> Oops, a couple of missing brackets in the previous reply:
>>
>>
>> foo<-function(x){
>> temp=x[x>0]
>> if(length(temp)>=3) sum(temp[1:3])
>> else sum(temp)
>> } #<----This was missing in the previous post
>>
>>
>> set.seed(2)
>> mat<-matrix(sample(0:4, 25, replace=T, prob=c(1/2,rep(1/8,4))), ncol=5)
>> #add a right parenthesis.
>> mat
>>
>> On Tue, May 21, 2013 at 3:47 AM, Xiao He <praguewaterme...@gmail.com>wrote:
>>
>>> Does this work? Probably not the fastest, but I think it does the job.
>>>
>>> foo<-function(x){
>>> temp=x[x>0]
>>> if(length(temp)>=3) sum(temp[1:3])
>>> else sum(temp)
>>>
>>> set.seed(2)
>>> mat<-matrix(sample(0:4, 25, replace=T, prob=c(1/2,rep(1/8,4)), ncol=5)
>>> mat
>>>
>>> # [,1] [,2] [,3] [,4] [,5]
>>> #[1,] 0 1 2 4 3
>>> #[2,] 3 0 0 1 0
>>> #[3,] 2 4 4 0 4
>>> #[4,] 0 0 0 0 0
>>> #[5,] 1 2 0 0 0
>>>
>>>
>>> apply(mat, 1, foo) #Apply the function to each row of the matrix
>>> #[1] 7 4 10 0 3
>>>
>>>
>>>
>>> On Tue, May 21, 2013 at 2:16 AM, José Verhoeven <j...@memo2.nl> wrote:
>>>
>>>> Hi there,
>>>> I've got this matrix D with, say 10 rows and 20 columns. For each row I
>>>> want
>>>> to sum the first 3 non zero elements and put them in a vector z.
>>>>
>>>> So if the first row D[1,] is
>>>> 0 3 5 0 8 9 3 2 4 0
>>>>
>>>> then I want z
>>>> z<-D[1,2]+D[1,3]+D[1,5]
>>>>
>>>> But if there are less than 3 non zero elements, those should be summed.
>>>> If
>>>> there are no non zero elements, the result must be zero.
>>>>
>>>> So if the first row D[1,] is
>>>> 0 0 3 0 1 0 0 0 0 0
>>>>
>>>> then I want z
>>>> z<-D[1,3]+D[1,5]
>>>>
>>>> Hope someone can help me out!
>>>>
>>>> [[alternative HTML version deleted]]
>>>>
>>>> ______________________________________________
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>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>>
>>>
>>
>
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