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local average

3 messages · jhainm@fas.harvard.edu, Zhen Pang, Rich FitzJohn

jhainm@fas.harvard.edu
# 
Hello,

probably this isn't hard, but I can't get R to do this. Thanks for your
help!

Assume I have a matrix of two covariates:

n    <- 1000
Y    <- runif(n)
X    <- runif(n,min=0,max=100)
data <- cbind(Y,X)

Now, I would like to compute the local average of Y for each X interval 0-1,
1-2, 2-3, ... 99-100. In other words, I would like to obtain 100 (local)
Ybars, one for each X interval with width 1.

Also, I would like to do the same but instead of local means of Y obtain
local medians of Y for each X interval.

Best,
Jens
Zhen Pang
# 
a<-sapply(1:100,function(x)mean(Y[X<x & X>x-1]))
b<-sapply(1:100,function(x)median(Y[X<x & X>x-1]))
Rich FitzJohn
# 
Hi,

cut() and tapply() are your friends:
tapply(Y, cut(X, 0:100, include.lowest=TRUE), mean)

To compute medians, just pass median to tapply().  You will get NAs
where no data is found in any bin.

Cheers,
Rich
On 4/21/05, Jens Hainmueller <jens_hainmueller at ksg05.harvard.edu> wrote: