plyr (version 1.8.3)

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

Description

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

Usage

alply(.data, .margins, .fun = NULL, ..., .expand = TRUE,
  .progress = "none", .inform = FALSE, .parallel = FALSE,
  .paropts = NULL, .dims = 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

.inform

produce informative error messages? This is turned off by default because it substantially slows processing speed, but is very useful for debugging

.parallel

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

.paropts

a list of additional options passed into the foreach function when parallel computation is enabled. This is important if (for example) your code relies on external data or packages: use the .e

.dims

if TRUE, copy over dimensions and names from input.

Value

• list of results

Input

This function splits matrices, arrays and data frames by dimensions

Output

If there are no results, then this function will return a list of length 0 (list()).

Details

The list will have "dims" and "dimnames" corresponding to the margins given. For instance alply(x, c(3,2), ...) where x has dims c(4,3,2) will give a result with dims c(2,3).

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/.

See Also

Other array input: a_ply; aaply; adply

Other list output: dlply; llply; mlply

Examples

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