Code parses monthly National Climatic Data Center Local Climatological Data reports (downloaded as .txt files)

parseMonthlyLCD.R

### Script to parse NCDC LCD comma-separated .txt files
parseMonthlyLCD <- function(txt_list) {
  # function takes a vector of comma separated filenames for NCDC LCD data (https://www.ncdc.noaa.gov/IPS/lcd/lcd.html)
  # returns a summary of monthly meteorological data
  # this seems to work at least back to 2009, but NCDC formatting is inconsistent, so use this code with caution
  
  # usage example: 
  # download .txt files from https://www.ncdc.noaa.gov/IPS/lcd/lcd.html
  # input_files <- list.files(path = "C:/RDATA/NCDC/NewOrleans/2013", full.names = TRUE, pattern = ".txt") # find .txts in a directory
  # parseMonthlyLCD(input_files)
  
  for (i in 1:length(txt_list)) {
    fullData <- suppressWarnings(readLines(txt_list[i]))
    
     # line containing summary data varies depending on the number of days in the month
     for (j in 27:37) {
       a <- as.numeric(strsplit(as.character(fullData[j]), ",")[[1]][1])
       b <- as.numeric(strsplit(as.character(fullData[j - 1]), ",")[[1]][1])
       if ((a != (b + 1)) | (is.na(a))) break
     }
    
    
    tempDat <- data.frame(t(as.numeric(strsplit(as.character(fullData[j]), ",")[[1]])))
    
    if (ncol(tempDat) == 20) {
      aggData    <- tempDat[c(2:4, 6:9, 13:20)]
      } else if (ncol(tempDat) > 15) {
      length_val <- ncol(tempDat)
      aggData    <- tempDat[c(2:4, 6:9, (length_val-7):length_val)]
      } else if (ncol(tempDat) == 15) {
      aggData    <- tempDat
      } else print(paste0("error: length of line ", j, " is ", ncol(tempDat), 
                        ". filename: ", txt_list[i]))
    
    
    names(aggData) <- c("meanDailyMaxTemp", "meanDailyMinTemp", "meanDailyMeanTemp", "meanDailyDewPt", "meanDailyWetBulb", "meanDailyHDD", 
                        "meanDailyCDD", "totalSnow_wtrEquiv", "totalSnow", "totalPrecip", "meanDailyinHg_stn", "meanDailyinHg_seaLevel", 
                        "meanResultantSpeed", "meanResultantDirection", "meanDailyWindSpeed")
    # extract station identifier, located in parentheses
    aggData$station   <- regmatches(as.character(fullData[2]), gregexpr("(?<=\\().*?(?=\\))", as.character(fullData[2]), perl=T))[[1]]
    stnDeets          <- strsplit(as.character(fullData[1]), "  ")[[1]]
    aggData$location  <- substr(stnDeets[length(stnDeets)], 1, nchar(stnDeets[length(stnDeets)]) - 1)
    aggData$moYr      <- as.Date(paste0(substr(stnDeets[1], 2, nchar(stnDeets[1])),  "-01"), format = "%B %Y-%d")
    
    if (i > 1) {
      output <- rbind(output, aggData)
    } else {
      output <- aggData
    }
  }
  
  # convert to metric
  output[, 1:5] <- (output[, 1:5] - 32) * 5/9            # convert degrees F to Celsius
  output[, 8:10] <- (output[, 8:10] * 2.54)              # convert inches to centimeters
  output[, c(13, 15)] <- (output[, c(13, 15)] * 0.44704) # convert mph to meters per sec
  
  output
}