Quick CSV to JSON in Swift

tsv_to_json.swift

import Foundation

// Swift 2.0

// poor man's parsers for (TSV) tab-separated value files
// for something more full-featured, the best avenue is CHCSVParser

/**
Reads a multiline, tab-separated String and returns an Array<NSictionary>, taking column names from the first line or an explicit parameter
*/
func JSONObjectFromTSV(tsvInputString:String, columnNames optionalColumnNames:[String]? = nil) -> Array<NSDictionary>
{
  let lines = tsvInputString.componentsSeparatedByString("\n")
  guard lines.isEmpty == false else { return [] }
  
  let columnNames = optionalColumnNames ?? lines[0].componentsSeparatedByString("\t")
  var lineIndex = (optionalColumnNames != nil) ? 0 : 1
  let columnCount = columnNames.count
  var result = Array<NSDictionary>()
  
  for line in lines[lineIndex ..< lines.count] {
    let fieldValues = line.componentsSeparatedByString("\t")
    if fieldValues.count != columnCount {
      //      NSLog("WARNING: header has %u columns but line %u has %u columns. Ignoring this line", columnCount, lineIndex,fieldValues.count)
    }
    else
    {
      result.append(NSDictionary(objects: fieldValues, forKeys: columnNames))
    }
    lineIndex = lineIndex + 1
  }
  return result
}

/**
commmand-line wrapper

USAGE:
# if file.tsv does not have field headers
$ xcrun swift tsv_to_json.swift fieldname1 fieldName2 < file.tsv > output.json

# if file.tsv does have field headers
$ xcrun swift tsv_to_json.swift < file.tsv > output.json

*/
func mymain()
{
  let columnNames:[String]? = Process.arguments.count > 1 ? Array(Process.arguments[1..<Process.arguments.count]) : nil
  
  let stdin = NSFileHandle.fileHandleWithStandardInput()
  let inData = stdin.readDataToEndOfFile()
  let inString = NSString(data:inData,encoding:NSUTF8StringEncoding)! as String
  
  let outJSONObject =  JSONObjectFromTSV(inString,columnNames:columnNames)

  do {
    let outData = try NSJSONSerialization.dataWithJSONObject(outJSONObject,options:.PrettyPrinted)
    let stdout = NSFileHandle.fileHandleWithStandardOutput()
    stdout.writeData(outData)
    stdout.closeFile()
  }
  catch _ {
    NSLog("Error trying to deserialize JSON Object")
  }
}

// mymain()

Thanks for taking a stab at this!

Updated to support Swift 5.

// Swift 2.0
// poor man's parsers for (TSV) tab-separated value files
// for something more full-featured, the best avenue is CHCSVParser
/**
Reads a multiline, tab-separated String and returns an Array<NSictionary>, taking column names from the first line or an explicit parameter
*/
func JSONObjectFromTSV(tsvInputString:String, columnNames optionalColumnNames:[String]? = nil) -> Array<NSDictionary>
{
  let lines = tsvInputString.components(separatedBy: "\n")
  guard lines.isEmpty == false else { return [] }
  
  let columnNames = optionalColumnNames ?? lines[0].components(separatedBy: "\t")
  var lineIndex = (optionalColumnNames != nil) ? 0 : 1
  let columnCount = columnNames.count
  var result = Array<NSDictionary>()
  
  for line in lines[lineIndex ..< lines.count] {
    let fieldValues = line.components(separatedBy: "\t")
    if fieldValues.count != columnCount {
      //      NSLog("WARNING: header has %u columns but line %u has %u columns. Ignoring this line", columnCount, lineIndex,fieldValues.count)
    }
    else
    {
        result.append(NSDictionary(objects: fieldValues, forKeys: columnNames as [NSCopying]))
    }
    lineIndex = lineIndex + 1
  }
  return result
}

/**
commmand-line wrapper
USAGE:
# if file.tsv does not have field headers
$ xcrun swift tsv_to_json.swift fieldname1 fieldName2 < file.tsv > output.json
# if file.tsv does have field headers
$ xcrun swift tsv_to_json.swift < file.tsv > output.json
*/
func mymain()
{
    let columnNames:[String]? = Process.init().arguments?.count ?? 0 > 1 ? Array(Process.init().arguments?[1..<(Process.init().arguments?.count ?? 0)] ?? []) : nil
    
    let stdin = FileHandle.standardInput
  let inData = stdin.readDataToEndOfFile()
    let inString = NSString(data:inData,encoding:String.Encoding.utf8.rawValue)! as String
  
    let outJSONObject =  JSONObjectFromTSV(tsvInputString: inString,columnNames:columnNames)

  do {
    let outData = try JSONSerialization.data(withJSONObject: outJSONObject,options:.prettyPrinted)
    let stdout = FileHandle.standardOutput
    stdout.write(outData)
    stdout.closeFile()
  }
  catch _ {
    NSLog("Error trying to deserialize JSON Object")
  }
}

// mymain()