Here is a solution using dplyr
require(data.table)
dt - as.data.table(mtcars)
library(dplyr)
library(tidyr)
dt %%
group_by(carb, cyl) %%
summarise(WM = weighted.mean(x = mpg, w = wt)) %%
spread(cyl, WM)
Best regards,
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
Forest
team Biometrie Kwaliteitszorg / team Biometrics Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey
2015-07-20 20:52 GMT+02:00 Bos, Roger roger@rothschild.com:
I am trying to figure out how to use dcast.data.table with a function with
multiple arguments. Here is my reproducible example for a simple function
of one argument:
require(data.table)
dt - as.data.table(mtcars)
dcast.data.table(dt, carb ~ cyl, value.var='mpg', fun=mean)
If I instead want to use, say, weighted.mean(x, w), how do I do so?
The docs say
...
Any other arguments that maybe passed to the aggregating function.
So I tried:
dcast.data.table(dt, carb ~ cyl, value.var='mpg', fun=weighted.mean,
w=wt)
Error in weighted.mean.default(data[[value.var]][0], ...) :
'x' and 'w' must have the same length
The docs also say that value.var can be a list, so I tried that:
In cases where value.var is a list, the function should be able to handle
a list input and provide a single value or list of length one as output.
dcast.data.table(dt, carb ~ cyl, value.var=list('mpg','wt'),
fun=weighted.mean)
Error in dcast.data.table(dt, carb ~ cyl, value.var = list(mpg, wt), :
'value.var' must be a character vector of length 1.
I didn't actually expect that to work, but without an example I don't know
what else to try. Any hints would be greatly appreciated.
Thanks,
Roger
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