# rolling 

  # x = vector of values
  # n = window size
  # callback = function target, in the format "function(x){sd(x)}" or "function(x){mean(x)}"


'# 04 / 11 /2025

ℹ In group 1: `uniqueID = "PYR11_BASE_01"`.
Caused by error in `x[i:(i + n - 1)]`:
! only 0s may be mixed with negative subscripts

Added: '


lag_apply <- function(x, n, callback){
  k = length(x);
  result = rep(NA, k);
  for(i in 1 : (k - n + 1)){ # 1 : (k - n + 1)
    result[i+(n-1)] <- callback(x[i:(i + n-1)]);
  }    
  return(result);
}

# lag_apply(subset(mean_stand_export_list, PLOT == "PYR00")$nTrees.ha, 20, function(x){mean(x)})