如何将文本列从 DBF 文件转换为数字

Question

我有几个 DBF 文件需要稍后处理，但文件中的所有列都是字符。

允许我这样做的代码是这样的：

library("shapefiles")
library("data.table")
library("reshape2")
library("stringr")

as.numeric.factor <- function (parFactor)
{
  isAllNumerical <- all( suppressWarnings(!is.na(as.numeric( levels(parFactor)) )) == TRUE)
  if (isAllNumerical == TRUE)
  {
    parFactor <- as.numeric( as.character( parFactor ) )
  }
  else
  {
    parFactor <- FALSE
  }
  return (parFactor)
}

dbf.factorsToNumeric <- function (dataFrame, colsToConvert)
{
  for (colName in colsToConvert)
  {
    numColum <- as.numeric.factor( dataFrame[,colName] )
    if (class(numColum) != "logical")
    {
      colPosition <- match (colName, names(dataFrame))
      dataTypes <- attr(dataFrame, "data_types")
      dataTypes[colPosition] <- "N"
      attr(dataFrame, "data_types") <- dataTypes
      dataFrame[,colName] <- numColum
    }
  }
  return(dataFrame)
}

filePath <- file.choose() #assign file path to a variable
survey <- read.dbf( filePath , header = TRUE) #LoadFile
print(survey$header$num.records) # Print number of records

colNames <- names(survey$dbf) #get all column names in dataset
survey$dbf <- dbf.factorsToNumeric (survey$dbf, colNames) #convert required columns into numeric
outFilePath <- str_replace(filePath, ".dbf|.DBF", "2.dbf") #replace original filename to avoid overwriting
write.dbf(survey, outFilePath, FALSE) #write new file

无论如何我可以避免两次“as.numeric”转换吗？

谢谢。

Answer 1

这是 tryCatch 的理想场所：

as.numeric.factor <- function (x) {
    allNumeric  <-  TRUE
    # try to convert the levels to numeric
    tryCatch(vals  <-  as.numeric(levels(x)),
             # if there is a warning, set `allNumeric` to FALSE
             warning=function(err)
                 if(err$message == 'NAs introduced by coercion')
                     allNumeric<<-FALSE
                 #raise an error if the warning isn't the one we expected.
                 else stop(err))
    if(allNumeric)
        # if the levels are all numeric, return a numeric vector
        return(vals[unclass(x)])
    else
        # otherwise return the oringinal factor
        return(x)
}