plyr (version 1.5.2)

alply: Split array, apply function, and return results in a list.

Description

Split array, apply function, and return results in a list. For each slice of an array, apply function then combine results into a list

Usage

alply(.data, .margins, .fun, ..., .expand=TRUE,
    .progress="none", .parallel=FALSE)

Arguments

.data

matrix, array or data frame to be processed

.margins

a vector giving the subscripts to split up data by. 1 splits up by rows, 2 by columns and c(1,2) by rows and columns, and so on for higher dimensions

.fun

function to apply to each piece

...

other arguments passed on to .fun

.expand

if .data is a data frame, should output be 1d (expand = FALSE), with an element for each row; or nd (expand = TRUE), with a dimension for each variable.

.progress

name of the progress bar to use, see create_progress_bar

.parallel

if TRUE, apply function in parallel, using parallel backend provided by foreach

Value

• list of results

Details

All plyr functions use the same split-apply-combine strategy: they split the input into simpler pieces, apply .fun to each piece, and then combine the pieces into a single data structure. This function splits matrices, arrays and data frames by dimensions and combines the result into a list. If there are no results, then this function will return a list of length 0 (list()).

alply is somewhat similar to apply for cases where the results are not atomic.

References

Hadley Wickham (2011). The Split-Apply-Combine Strategy for Data Analysis. Journal of Statistical Software, 40(1), 1-29. http://www.jstatsoft.org/v40/i01/.

Examples

alply(ozone, 3, quantile)
alply(ozone, 3, function(x) table(round(x)))