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df <-data.frame(id=c(1L,1L,2L,3L,2L,3L,4L),brand=c('a','a','b','c','d','a','b'),quantity=c(
2L,1L,5L,10L,11L,1L,2L),stringsAsFactors=F);

  id brand quantity
1  1     a        2
2  1     a        1
3  2     b        5
4  3     c       10
5  2     d       11
6  3     a        1
7  4     b        2

this is the data frame

if I use the following command

sparse_matrix1 <- reshape2::dcast(df, df$id~df$brand )

I get the following output

  df$id a b c d
1     1 2 0 0 0
2     2 0 1 0 1
3     3 1 0 1 0
4     4 0 1 0 0

It is taking only first entry for the result but it is not giving the sum of the first two entries.

Is there a way such that, I get answer as 3 (i.e. 2+1 sum of quantity for first and second entries) brand =3 and id = 1.

The output should be 

  df$id a b c d
1     1 3 0 0 0
2     2 0 1 0 1
3     3 1 0 1 0
4     4 0 1 0 0

Thanks in advance.

Maddy
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1 Answers1

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Thanks to "mtoto"

I forgot to add fun.aggregate=sum in the function.

the code becomes

sparse_matrix1 <- reshape2::dcast(df, df$id~df$brand, fun.aggregate = sum )
Maddy
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