popEpi (version 0.2.1)

expr.by.cj: Tabulate counts and other functions with multiple factors into a long-format table

Description

Like ltable except faster and unrobust. For advanced users.

Usage

expr.by.cj(data, by.vars = "sex", expr = list(obs = .N), subset = NULL,
  .SDcols, ...)

Arguments

data

a data.table

by.vars

a character string vector specifying the names of variables, by the combinations of which to evaluate the given expr

expr

an arbitrary expression utilizing any available function on any variable available in the data

subset

a logical condition; data is limited accordingly before evaluating expr

.SDcols

advanced; passed to inside the data.table's brackets DT[, , ...]; see data.table

...

advanced; other arguments passed to inside the data.table's brackets DT[, , ...]; see data.table

Examples

sr <- copy(sire)
sr$agegroup <- cut(sr$dg_age, breaks=5)
## counts by default
expr.by.cj(sr, "agegroup")

## any arbitrary expression can be given
expr.by.cj(sr, "agegroup", list(mage = mean(dg_age)))
expr.by.cj(sr, "agegroup", list(mage = mean(dg_age), vage = var(dg_age)))

## only uses levels of by.vars present in data
expr.by.cj(sr, "agegroup", list(mage = mean(dg_age), vage = var(dg_age)),
           subset = dg_age < 70)