Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

How to summarise data by group with weighted mean?

Tags:

r

With

xa=aggregate(x$avg,by=list(x$value),FUN=weighted.mean,w=x$weight)

gives me an error

Error in weighted.mean.default(X[[1L]], ...) :    'x' and 'w' must
have the same length

But

weighted.mean(x$avg,w=x$weight);

works fine.

like image 707
xiaodai Avatar asked Aug 22 '11 09:08

xiaodai


People also ask

What is the use of weighted mean in statistics?

In calculating a simple average, or arithmetic mean, all numbers are treated equally and assigned equal weight. But a weighted average assigns weights that determine in advance the relative importance of each data point. A weighted average is most often computed to equalize the frequency of the values in a data set.


1 Answers

As suggested on an old R thread, you can use by instead:

wt <- c(5,  5,  4,  1)/15
x <- c(3.7,3.3,3.5,2.8)
xx <- data.frame(avg=x, value=gl(2,2), weight=wt)
by(xx, xx$value, function(x) weighted.mean(x$avg, x$weight))
like image 89
chl Avatar answered Oct 20 '22 02:10

chl