plm (version 1.5-12)

pvar: Check for Cross-Sectional and Time Variation

Description

This function checks for each variable of a panel if it varies cross-sectionally and over time.

Usage

pvar(x, ...)
"pvar"(x, index = NULL, ...)
"pvar"(x, ...)
"print"(x, ...)

Arguments

x

a data.frame,

index

see pdata.frame,

...

further arguments.

Value

An object of class pvar containing the following elements:

id.var

a logical vector with TRUE values if the variable has individual variation, FALSE otherwise,

time.var

a logical vector with TRUE values if the variable has time variation, FALSE otherwise,

Details

pvar can be time consuming for ``big'' panels.

Examples

# Gasoline contains two variables which are individual and time indexes
# and are the first two variables
data("Gasoline", package = "plm")
pvar(Gasoline)

# Hedonic is an unbalanced panel, townid is the individual index;
# the drop.index argument is passed to pdata.frame
data("Hedonic", package = "plm")
pvar(Hedonic, "townid", drop.index = TRUE)

# same using pdata.frame
Hed <- pdata.frame(Hedonic, "townid", drop.index = TRUE)
pvar(Hed)