[R] Script for conditional sums of vectors

[arun]

Hi,
library(reshape2)
dcast(DF,a~b,value.var="c",sum)
#  a   1   2   3   4
#1 1 900 100 500 300
#2 2 300 900 200 100
A.K.
----- Original Message -----
From: Benjamin Gillespie <gybrg at leeds.ac.uk>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Monday, February 4, 2013 4:29 AM
Subject: [R] Script for conditional sums of vectors

Hi guys,

I hope you can help me with this (probably) simple query:

I have a data frame:

--------------------------

a=c(1,1,1,1,1,1,2,2,2,2,2,2)
b=c(1,1,1,2,3,4,1,1,2,2,3,4)
c=c(400,200,300,100,500,300,200,100,500,400,200,100)


data=data.frame(a=a,b=b,c=c)

--------------------------

And I would like to get the following output:

--------------------------

    b
a    1    2    3    4
1    900    100    500    300
2    300    900    200    100

--------------------------

The values in the output represent the sum of values "c" in data frame "data", for each "a" and "b" combination.

For example, where "a" = 1 and "b" = 1, the output is 400+200+300 = 900.

Please would anyone be able to provide a script to create my desired output?

Many thanks in advance,
        
Ben Gillespie
Research Postgraduate

School of Geography
University of Leeds
Leeds
LS2 9JT


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