Function to calculate growth rate

[spsanderson]

need a function to calculate growth rate of a series.

Function:

ts_growth_rate_vec <- function(.x, .scale = 100, .power = 1, .log_diff = FALSE,
                               .lags = 1){
  
  # Variables
  x <- as.vector(as.numeric(.x))
  s <- as.numeric(.scale)
  p <- as.numeric(.power)
  l <- as.numeric(.lags)
  ld <- as.logical(.log_diff)
  
  # Checks
  if (!is.vector(x) | !is.numeric(x)){
    rlang::abort(
      message = ".x must be a numeric vector",
      use_cli_format = TRUE
    )
  }
  
  if (!is.numeric(s) | !is.numeric(p) | !is.numeric(l)){
    rlang::abort(
      message = ".scale, .power and .lags must all be numeric",
      use_cli_format = TRUE
    )
  }
  
  if (!is.logical(ld)){
    rlang::abort(
      message = ".log_diff must be either TRUE or FALSE",
      use_cli_format = TRUE
    )
  }
  
  if (l == 0){
    rlang::abort(
      message = ".lags must be an integer that is either greater than or less than 0",
      use_cli_format = TRUE
    )
  }
  
  # Calculation
  if (l < 0){
    if (ld) {
      return(log(x / dplyr::lead(x, -l)) * s)
    } else {
      return(((x / dplyr::lead(x, -l))^p - 1) * s)
    }
  } else if (ld){
    return(log(x/dplyr::lag(x, l)) * s)
  } else {
    return(((x / dplyr::lag(x, l))^p - 1) * s)
  }
}

Example:

> x <- AirPassengers
> ts_growth_rate_vec(x) |> head(12)
 [1]         NA   5.357143  11.864407  -2.272727  -6.201550  11.570248   9.629630   0.000000
 [9]  -8.108108 -12.500000 -12.605042  13.461538
> ts_growth_rate_vec(x, .log_diff = TRUE) |> head(12)
 [1]         NA   5.218575  11.211730  -2.298952  -6.402186  10.948423   9.193750   0.000000
 [9]  -8.455739 -13.353139 -13.473259  12.629373
> ts_growth_rate_vec(x, .lags = 2) |> head(12)
 [1]          NA          NA  17.8571429   9.3220339  -8.3333333   4.6511628  22.3140496
 [8]   9.6296296  -8.1081081 -19.5945946 -23.5294118  -0.8403361
> ts_growth_rate_vec(x, .lags = -1) |> head(12)
 [1]  -5.084746 -10.606061   2.325581   6.611570 -10.370370  -8.783784   0.000000   8.823529
 [9]  14.285714  14.423077 -11.864407   2.608696
> ts_growth_rate_vec(x, .lags = -2) |> head(12)
 [1] -15.1515152  -8.5271318   9.0909091  -4.4444444 -18.2432432  -8.7837838   8.8235294
 [8]  24.3697479  30.7692308   0.8474576  -9.5652174  -6.3492063

ts_growth_rate_vec(AirPassengers, 100, 1) |>
  plot(type = "l")