Year-on-year (or compound) growth rate — growth

Adds a growth-rate column to a panel: either the period-over-period change ("yoy") or the compound annual growth rate from the first observed year ("cagr"), computed per country.

Usage

growth_rate(data, value, type = c("yoy", "cagr"), suffix = "_growth")

Arguments

data: A panel with iso3c and year.
value: The value column (unquoted).
type: "yoy" (default, period-over-period) or "cagr" (compound annual growth rate vs. the first non-NA year). "cagr" needs a positive ratio at both ends, so a negative value gives NA for that row (with a warning) and a non-positive base year gives NA for that country; a value of exactly 0 is a legitimate annualised -100%. "yoy" is a plain ratio change and is defined for negative values.
suffix: Suffix for the new column (default "_growth").

Value

data with a growth-rate column added (a proportion, so 0.03 = 3%). Rows come back sorted by iso3c then year: the calculation reads each country's series in time order, so a row-aligned vector held alongside data will no longer line up.

Examples

df <- data.frame(iso3c = "USA", year = 2000:2002, gdp = c(100, 110, 121))
growth_rate(df, gdp)
#> # A tibble: 3 × 4
#>   iso3c  year   gdp gdp_growth
#>   <chr> <int> <dbl>      <dbl>
#> 1 USA    2000   100     NA    
#> 2 USA    2001   110      0.100
#> 3 USA    2002   121      0.100