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 *************************************************************** This message and any attachments are for the intended recipient's use only. This message may contain confidential, proprietary or legally privileged information. No right to confidential or privileged treatment of this message is waived or lost by an error in transmission. If you have received this message in error, please immediately notify the sender by e-mail, delete the message, any attachments and all copies from your system and destroy any hard copies. You must not, directly or indirectly, use, disclose, distribute, print or copy any part of this message or any attachments if you are not the intended recipient.
Thierry Onkelinx
2015-Jul-21 07:52 UTC
[R] using dcast with a function of multiple arguments
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.bos at 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 > > > > *************************************************************** > This message and any attachments are for the intended recipient's use only. > This message may contain confidential, proprietary or legally privileged > information. No right to confidential or privileged treatment > of this message is waived or lost by an error in transmission. > If you have received this message in error, please immediately > notify the sender by e-mail, delete the message, any attachments and all > copies from your system and destroy any hard copies. You must > not, directly or indirectly, use, disclose, distribute, > print or copy any part of this message or any attachments if you are not > the intended recipient. > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >[[alternative HTML version deleted]]