navtest -> navpre (for preformatted)

comment on stuff

nav table.R

@@ -1,21 +1,29 @@
 
 buildGuide <- function() {
+  # Table of variables and their meaning
+  # Used to determine column width and header
   navguide <-htmlParse("http://www.ucm.es/info/cliwoc/content/CLIWOC15corelimit.htm")
   navtables <- readHTMLTable(navguide)
+  # This version has only one table but we subset the list to get the dataframe
   format <- navtables[[1]][-1, 1:3]
+  # coerce everything to character
   as.data.frame(matrix(as.character(unlist(format, recursive = FALSE, use.names = FALSE)), dim(format)), stringsAsFactors = FALSE)
 }
 
 
 buildNavdf <- function(ingest) {
+  # From http://www.ucm.es/info/cliwoc/cliwoc15.htm
   nav.limit <- 245195
+  # Location and name for data
   core.url <- "http://www.knmi.nl/cliwoc/download/CLIWOC15corelimit.zip"
   core.filename <- "CLIWOC15corelimit.txt"
   grabRemote <- function(create.dir = FALSE) {
     format.ref <- buildGuide()
     temp <- tempfile()
     download.file(core.url, temp)
     navin <- read.fwf(unz(temp, filename = core.filename),
+                      # format page has start/stop numbers
+                      # We need to convert these to widths
                       widths = c(diff(as.numeric(format.ref[,2])), 2),
                       col.names = format.ref[,1],
                       stringsAsFactors = FALSE,
@@ -33,10 +41,24 @@ buildNavdf <- function(ingest) {
          initial = grabRemote(create.dir = TRUE)
          )
 }
-navtest <- buildNavdf(ingest = "initial")
 
+navpre <- buildNavdf(ingest = "local")
 
-navtest <- navtest[, names(navtest) %in% c("YR", "MO", "DY", "HR", "LAT", "LON", "ID", "C1", "D")]
-navtest[, "Date"] <- as.Date(sprintf("%4.f-%02.f-%2.f", navtest[,"YR"], navtest[,"MO"], navtest[,"DY"]), format = "%Y-%m-%d")
+# Drops all but date/time, lat/long, ship ID, country and wind direction
+# May drop wind direction later but it might be fun to plot
+navpre <- navpre[, names(navpre) %in% c("YR", "MO", "DY", "HR", "LAT", "LON", "ID", "C1", "D")]
 
-navtest[, "HR"] <- sprintf("%04.f",navtest[,"HR"])
+# About 5 seconds faster than paste(). 
+navpre[, "Date"] <- as.Date(sprintf("%4.f-%02.f-%2.f", navpre[,"YR"], navpre[,"MO"], navpre[,"DY"]), format = "%Y-%m-%d")
+
+# Build Factor variables and convert lat/long
+navpre[, "Country"] <- as.factor(navpre[, "C1"])
+navpre[, "Month"] <- factor(month.name[navpre[, "MO"]], levels = month.name, ordered = FALSE)
+navpre[, "Lat"] <- navpre[, "LAT"]/100
+navpre[, "Long"] <- navpre[, "LON"]/100
+
+diff.lat <- diff(navpre[, "LAT"])
+diff.id <- diff(navpre[, "ID"])
+diff.date <- diff(navpre[, "Date"])
+
+single.diff <- diff.lat[diff.id == 0 & diff.date == 1]