[R] Use of the "by" command (clarification)

From: Economics Guy <economics.guy_at_gmail.com>
Date: Sat, 16 Jun 2007 18:55:54 -0400


Well apparently this has nothing to do with the gini() command.

I cannot get it to work for something as simple as sum()

Here is the little example I am playing with, maybe someone can help me find my error:

a<-c("A","B","C","A","B","C","A","A","C","B")

b<-c(23,6534,456,234,7,567,345,9,565,345)

c<-cbind(a,b)

by(c, a, function(x) sum(b))

and I get the output

INDICES: A
[1] 9085



INDICES: B
[1] 9085

INDICES: C

[1] 9085

Same problem as before. It is summing over the whole b vector rather than by the groups.

Anybody have any ideas on what I am doing wrong?

Thanks,

EG

On 6/16/07, Economics Guy <economics.guy_at_gmail.com> wrote:
>
> I have a data set that contains income data and a group identifier. Sort
> of like:
>
>
> DATA
>
> Group,Income
> A,2300
> B,6776
> A,6668
> A,6768
> B,9879
> C,5577
> A,7867
> (etc),(etc)
>
> I am trying to compute the gini coefficient for each group.
>
> I have tried the following and none seem to do the trick:
>
> 1)
>
> attach(DATA)
>
> by(DATA, group, function(x) gini(income))
>
>
> 2)
>
> attach(data)
>
> tapply(income, group, function(x) gini(income))
>
> Both of these return the same value for all groups. Like:
>
> group: A
> [1] 0.2422496
> ------------------------------------------------------------
> group: B
> [1] 0.2422496
> ------------------------------------------------------------
> group: C
> [1] 0.2422496
> ------------------------------------------------------------
> group: D
> [1] 0.2422496
>
> Any ideas on how I can make this work? I need the fastest way since I am
> gonna run a monte carlo based on this routine once I get the basics working.
>
>
> Thanks,
>
> EG

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