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 <smaxw...@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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