[R] Subtracting rows by id

[Kenn Konstabel]

Or without plyr:

# Dennis's sample data but with shortened names
ds <- data.frame(id = rep(1:3, each = 10),
                      value1 = sample(seq_len(100), 30, replace = TRUE))
k <- data.frame(id = 1:3, sv = c(1, 3, 5))

do.call(rbind,
      mapply( function(a,b) subset(ds, id==a)[-1:-b,], k$id, k$sv,
SIMPLIFY=FALSE)
      )


On Wed, May 25, 2011 at 10:58 PM, Dennis Murphy <djmuser at gmail.com> wrote:
> Hi:
>
> Interesting problem. Here's one approach:
>
> library(plyr)
> # Read in your datasets as data frames rather than matrices
> dataset1 <- data.frame(id1 = rep(1:3, each = 10),
>                       value1 = sample(seq_len(100), 30, replace = TRUE))
> dataset2 <- data.frame(id2 = 1:3, subtract.value = c(1, 3, 5))
>
> # The idea is to use the rows of dataset2 as parameters for
> # subsetting and removing the first n_i rows. The tail() function
> # serves the purpose:
> foo <- function(id2, subtract.value) tail(subset(dataset1, id1 ==
> id2), -subtract.value)
>
> # Use the mdply function in the plyr package:
>> mdply(dataset2, foo)[, -(1:2)]
>   id1 value1
> 1    1      2
> 2    1     55
> 3    1     18
> 4    1      4
> 5    1      3
> 6    1     76
> 7    1     74
> 8    1     21
> 9    1     97
> 10   2     19
> 11   2     49
> 12   2     20
> 13   2     73
> 14   2     79
> 15   2     95
> 16   2     52
> 17   3     60
> 18   3     58
> 19   3     68
> 20   3     59
> 21   3     13
>
>
> HTH,
> Dennis
>
> On Wed, May 25, 2011 at 9:55 AM, Sara Maxwell <smaxwell at ucsc.edu> wrote:
>> Dear R users,
>>
>> I have two datasets:
>>
>> id1 <- c(rep(1,10), rep(2,10), rep(3,10))
>> value1 <- sample(1:100, 30, replace=TRUE)
>> dataset1 <- cbind(id1,value1)
>>
>> id2 <- c(1,2,3)
>> subtract.value <- c(1,3,5)
>> dataset2 <- cbind(id2, subtract.value)
>>
>> I want to subtract the number of rows in the subtract.value that
>> corresponds to the id value in dataset1.  So for the 1 in id1, I want
>> to remove the first row, for 2 in id1 I want to remove the first 3
>> rows, for 3 in id1 I want to remove the first 5 rows, finally creating
>> a new dataframe with the remaining values.
>>
>> I am having trouble structuring a loop that can do this by the unique
>> ids in the first dataset while matching the ids in the datasets.
>>
>> Any thoughts would be greatly appreciated.
>>
>> Thank you,
>> Sara
>>
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>