R/zeroPad.r

In usgs/dataRetrieval: Retrieval Functions for USGS and EPA Hydrologic and Water Quality Data

#' Pad string with leading zeros
#'
#' Function to pad a string with leading zeros. Useful for parameter codes and USGS site IDs.
#'
#' @param x character 
#' @param padTo number Final desired length of the character
#' @keywords data import USGS web service
#' @return x character returned with leading zeros
#' @export
#' @examples
#' pCode <- '10'
#' correctPCode <- zeroPad(pCode,5)
#' pCodes <- c('100','1000','0','12345','1565465465465465')
#' correctPCodes <- zeroPad(pCodes,5)
#' pCodeNA <- c(1,2,NA)
#' padPCodeNA <- zeroPad(pCodeNA,4)
zeroPad <- function(x,padTo){
  if(padTo <= 1) return(x)
  
  numDigits <- nchar(x, keepNA = TRUE)
  padding <- padTo-numDigits
  
  if(anyNA(padding)){
    padding[is.na(padding)] <- 0
  }
  
  paddingZeros <- vapply(
      X = padding[padding > 0], 
      FUN = function(y) paste0(rep("0",y),collapse=""),
      FUN.VALUE = ""
  )
  
  x[padding > 0] <- paste0(paddingZeros,x[padding > 0])
  return(x)
}