Add lagged variables to a state panel — add

Adds a lagged version of each requested column, computed within each state (group_by(cow) or group_by(gw), matching the panel's coding system) after sorting by year — required for lags to be meaningful in panel data. Unlike a plain dplyr::lag(), the lag is NA wherever the preceding row is not exactly n years earlier, so gaps in the year sequence (e.g. after filtering with tidyr::drop_na()) do not silently produce a lag from the wrong year.

Usage

add_lag(panel, vars, n = 1)

Arguments

panel: A data frame produced by build_states_panel(), containing a cow or gw column and a year column.
vars: Character vector of column names in panel to lag.
n: Integer. Number of years to lag by. Default 1.

Value

The input panel with one additional column per entry in vars, named <var>_l, holding the value of <var> from n years earlier for the same state (or NA if that year is not present in panel).

Examples

panel <- build_states_panel(1990, 2000, coding_system = "cow") |>
  add_gdp() |>
  add_lag(vars = c("gdp_pcap", "gdp_growth"), n = 1)