reshape2 (version 1.4.2)

cast: Cast functions Cast a molten data frame into an array or data frame.

Description

Use acast or dcast depending on whether you want vector/matrix/array output or data frame output. Data frames can have at most two dimensions.

Usage

dcast(data, formula, fun.aggregate = NULL, ..., margins = NULL, subset = NULL, fill = NULL, drop = TRUE, value.var = guess_value(data))
acast(data, formula, fun.aggregate = NULL, ..., margins = NULL, subset = NULL, fill = NULL, drop = TRUE, value.var = guess_value(data))

Arguments

data

molten data frame, see melt.

formula

casting formula, see details for specifics.

fun.aggregate

aggregation function needed if variables do not identify a single observation for each output cell. Defaults to length (with a message) if needed but not specified.

...

further arguments are passed to aggregating function

margins

vector of variable names (can include "grand\_col" and "grand\_row") to compute margins for, or TRUE to compute all margins . Any variables that can not be margined over will be silently dropped.

subset

quoted expression used to subset data prior to reshaping, e.g. subset = .(variable=="length").

fill

value with which to fill in structural missings, defaults to value from applying fun.aggregate to 0 length vector

drop

should missing combinations dropped or kept?

value.var

name of column which stores values, see guess_value for default strategies to figure this out.

Details

The cast formula has the following format: x_variable + x_2 ~ y_variable + y_2 ~ z_variable ~ ... The order of the variables makes a difference. The first varies slowest, and the last fastest. There are a couple of special variables: "..." represents all other variables not used in the formula and "." represents no variable, so you can do formula = var1 ~ ..

Alternatively, you can supply a list of quoted expressions, in the form list(.(x_variable, x_2), .(y_variable, y_2), .(z)). The advantage of this form is that you can cast based on transformations of the variables: list(.(a + b), (c = round(c))). See the documentation for . for more details and alternative formats.

If the combination of variables you supply does not uniquely identify one row in the original data set, you will need to supply an aggregating function, fun.aggregate. This function should take a vector of numbers and return a single summary statistic.

See Also

melt, http://had.co.nz/reshape/

Examples

#Air quality example
names(airquality) <- tolower(names(airquality))
aqm <- melt(airquality, id=c("month", "day"), na.rm=TRUE)

acast(aqm, day ~ month ~ variable)
acast(aqm, month ~ variable, mean)
acast(aqm, month ~ variable, mean, margins = TRUE)
dcast(aqm, month ~ variable, mean, margins = c("month", "variable"))

library(plyr) # needed to access . function
acast(aqm, variable ~ month, mean, subset = .(variable == "ozone"))
acast(aqm, variable ~ month, mean, subset = .(month == 5))

#Chick weight example
names(ChickWeight) <- tolower(names(ChickWeight))
chick_m <- melt(ChickWeight, id=2:4, na.rm=TRUE)

dcast(chick_m, time ~ variable, mean) # average effect of time
dcast(chick_m, diet ~ variable, mean) # average effect of diet
acast(chick_m, diet ~ time, mean) # average effect of diet & time

# How many chicks at each time? - checking for balance
acast(chick_m, time ~ diet, length)
acast(chick_m, chick ~ time, mean)
acast(chick_m, chick ~ time, mean, subset = .(time < 10 & chick < 20))

acast(chick_m, time ~ diet, length)

dcast(chick_m, diet + chick ~ time)
acast(chick_m, diet + chick ~ time)
acast(chick_m, chick ~ time ~ diet)
acast(chick_m, diet + chick ~ time, length, margins="diet")
acast(chick_m, diet + chick ~ time, length, drop = FALSE)

#Tips example
dcast(melt(tips), sex ~ smoker, mean, subset = .(variable == "total_bill"))

ff_d <- melt(french_fries, id=1:4, na.rm=TRUE)
acast(ff_d, subject ~ time, length)
acast(ff_d, subject ~ time, length, fill=0)
dcast(ff_d, treatment ~ variable, mean, margins = TRUE)
dcast(ff_d, treatment + subject ~ variable, mean, margins="treatment")
if (require("lattice")) {
 lattice::xyplot(`1` ~ `2` | variable, dcast(ff_d, ... ~ rep), aspect="iso")
}