Own impute

own_imp <- function(dt){
  for (column in 1:ncol(dt)){
    corr <- sapply(c(names(dt[,-column])),
                   function(x) cor(dt[,column], dt[,x],  use = "p"))

    corr_dec <- sort(corr, decreasing = TRUE)
    imp.use <- names(corr_dec[1])

    lm.cf <- lm(reformulate(imp.use, colnames(dt[column])), dt)$coef

    dt[, column] <- ifelse(is.na(dt[, column]), lm.cf[1] + dt[[imp.use]] *lm.cf[2], dt[,column])
  }
  return(dt)
}

file = "https://www.dropbox.com/s/jw8oqc9816ul8jq/GRP_outside_d20.csv?dl=1"
GRP_data = read.csv(file = file)

new_data <- own_imp(GRP_data)