[R] All a column to a data frame with a specific condition

From: Yi <liuyi.feier_at_gmail.com>
Date: Fri, 25 Jun 2010 17:27:54 -0700


Hi, folks,

Please first look at the codes:

plan_a=c('apple','orange','apple','apple','pear','bread') plan_b=c('bread','bread','orange','bread','bread','yogurt') value=1:6
data=data.frame(plan_a,plan_b,value)

library(plyr)
library(reshape)
mm=melt(data, id=c('plan_a','plan_b'))

sum_plan_a=cast(mm,plan_a~variable,sum)

### I would like to add a new column to the data.frame named 'data', with
the same sum of value for the same type of plan_a
### The result should come up like this:

   plan_a plan_b value sum_plan_a

1  apple  bread      1        8
2 orange  bread     2        2
3  apple orange     3        8
4  apple  bread      4        8
5   pear  bread      5         5
6  bread yogurt     6         6

Any tips?

Thank you.

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