R: Extract the indexes of panel data

index {plm} | R Documentation

## Extract the indexes of panel data

### Description

This function extracts the information about the structure of the individual and time dimensions of panel data.

### Usage

    ## S3 method for class 'pindex'
    index(x, which = NULL, ...)
    ## S3 method for class 'pdata.frame'
    index(x, which = NULL, ...)
    ## S3 method for class 'pseries'
    index(x, which = NULL, ...)
    ## S3 method for class 'panelmodel'
    index(x, which = NULL, ...)

### Arguments

`x` | an object of class `"pindex"`, `"pdata.frame"`, `"pseries"` or `"panelmodel"`,
`which` | the index(es) to be extracted (see details),
`...` | further arguments.

### Details

panel data are stored in a `"pdata.frame"` which has an `"index"` attribute. Fitted models in `"plm"` has a `"model"` element which is also a `"pdata.frame"` and therefore also have an `"index"` attribute. Finally, each series in a `"pdata.frame"` is of class `"pseries"`, which also has this `"index"` attribute. `"index"` methods are available for all these objects. The argument `"which"` indicates which index should be extracted. If `which = NULL`, both indexes are extracted, but `"which"` can also be a vector of length 1 or 2 containing either characters (the names of the individual variable and/or of the time variable or `"id"` and `"time"`) or integers (1 for the individual index and 2 for the time index.)

### Value

a vector or a `"data.frame"` containing either one index or both indexes.

### Author(s)

Yves Croissant

### See Also

`plm`

### Examples

    data("Grunfeld", package = "plm")
    Gr <- pdata.frame(Grunfeld, index = c("firm", "year"))
    m <- plm(inv ~ value + capital, data = Gr)
    index(Gr, "firm")
    index(Gr, "time")
    index(Gr$inv, c(2, 1))
    index(m, "id")

[Package plm version 1.6-5 Index]