# std/parsecsv

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This module implements a simple high performance CSV (comma separated value) parser.

# Basic usage

    import std/parsecsv
    from std/os import paramStr
    from std/streams import newFileStream

    var s = newFileStream(paramStr(1), fmRead)
    if s == nil:
      quit("cannot open the file" & paramStr(1))

    var x: CsvParser
    open(x, s, paramStr(1))
    while readRow(x):
      echo "new row: "
      for val in items(x.row):
        echo "##", val, "##"
    close(x)

For CSV files with a header row, the header can be read and then used as a reference for item access with rowEntry:

    import std/parsecsv

    # Prepare a file
    let content = """One,Two,Three,Four
    1,2,3,4
    10,20,30,40
    100,200,300,400
    """
    writeFile("temp.csv", content)

    var p: CsvParser
    p.open("temp.csv")
    p.readHeaderRow()
    while p.readRow():
      echo "new row: "
      for col in items(p.headers):
        echo "##", col, ":", p.rowEntry(col), "##"
    p.close()

# See also

- streams module for using open proc and other stream processing (like close proc)
- parseopt module for a command line parser
- parsecfg module for a configuration file parser
- parsexml module for a XML / HTML parser
- parsesql module for a SQL parser
- other parsers for other parsers

# Imports

lexbase, streams, syncio, os

# Types

    CsvError = object of IOError

  An exception that is raised if a parsing error occurs. Source Edit

    CsvParser = object of BaseLexer
      row*: CsvRow
      headers*: seq[string]

  The parser object.

  It consists of two public fields:

  - `row` is the current row
  - `headers` are the columns that are defined in the csv file (read using readHeaderRow). Used with rowEntry).
  Source Edit

    CsvRow = seq[string]

  A row in a CSV file. Source Edit

# Procs

    proc close(self: var CsvParser) {.inline, ...raises: [IOError, OSError],
                                      tags: [WriteIOEffect], forbids: [].}

  Closes the parser `self` and its associated input stream. Source Edit

    proc open(self: var CsvParser; filename: string; separator = ','; quote = '\"';
              escape = '\x00'; skipInitialSpace = false) {.
        ...raises: [CsvError, IOError, OSError], tags: [ReadIOEffect], forbids: [].}

  Similar to the other open proc, but creates the file stream for you.

  Example:

      from std/os import removeFile
      writeFile("tmp.csv", "One,Two,Three\n1,2,3\n10,20,300")
      var parser: CsvParser
      parser.open("tmp.csv")
      parser.close()
      removeFile("tmp.csv")

  Source Edit

    proc open(self: var CsvParser; input: Stream; filename: string; separator = ',';
              quote = '\"'; escape = '\x00'; skipInitialSpace = false) {.
        ...raises: [IOError, OSError], tags: [ReadIOEffect], forbids: [].}

  Initializes the parser with an input stream. `Filename` is only used for nice error messages. The parser's behaviour can be controlled by the diverse optional parameters:
  - `separator`: character used to separate fields
  - `quote`: Used to quote fields containing special characters like `separator`, `quote` or new-line characters. '\0' disables the parsing of quotes.
  - `escape`: removes any special meaning from the following character; '\0' disables escaping; if escaping is disabled and `quote` is not '\0', two `quote` characters are parsed one literal `quote` character.
  - `skipInitialSpace`: If true, whitespace immediately following the `separator` is ignored.

  See also:

  - open proc which creates the file stream for you

  Example:

      import std/streams
      var strm = newStringStream("One,Two,Three\n1,2,3\n10,20,30")
      var parser: CsvParser
      parser.open(strm, "tmp.csv")
      parser.close()
      strm.close()

  Source Edit

    proc processedRows(self: var CsvParser): int {.inline, ...raises: [], tags: [],
        forbids: [].}

  Returns number of the processed rows.

  But even if readRow arrived at EOF then processed rows counter is incremented.

  Example:

      import std/streams

      var strm = newStringStream("One,Two,Three\n1,2,3")
      var parser: CsvParser
      parser.open(strm, "tmp.csv")
      doAssert parser.readRow()
      doAssert parser.processedRows() == 1
      doAssert parser.readRow()
      doAssert parser.processedRows() == 2
      ## Even if `readRow` arrived at EOF then `processedRows` is incremented.
      doAssert parser.readRow() == false
      doAssert parser.processedRows() == 3
      doAssert parser.readRow() == false
      doAssert parser.processedRows() == 4
      parser.close()
      strm.close()

  Source Edit

    proc readHeaderRow(self: var CsvParser) {....raises: [IOError, OSError, CsvError],
        tags: [ReadIOEffect], forbids: [].}

  Reads the first row and creates a look-up table for column numbers See also:
  - rowEntry proc

  Example:

      import std/streams

      var strm = newStringStream("One,Two,Three\n1,2,3")
      var parser: CsvParser
      parser.open(strm, "tmp.csv")

      parser.readHeaderRow()
      doAssert parser.headers == @["One", "Two", "Three"]
      doAssert parser.row == @["One", "Two", "Three"]

      doAssert parser.readRow()
      doAssert parser.headers == @["One", "Two", "Three"]
      doAssert parser.row == @["1", "2", "3"]

      parser.close()
      strm.close()

  Source Edit

    proc readRow(self: var CsvParser; columns = 0): bool {.
        ...raises: [IOError, OSError, CsvError], tags: [ReadIOEffect], forbids: [].}

  Reads the next row; if `columns` > 0, it expects the row to have exactly this many columns. Returns false if the end of the file has been encountered else true.

  Blank lines are skipped.

  Example:

      import std/streams
      var strm = newStringStream("One,Two,Three\n1,2,3\n\n10,20,30")
      var parser: CsvParser
      parser.open(strm, "tmp.csv")
      doAssert parser.readRow()
      doAssert parser.row == @["One", "Two", "Three"]
      doAssert parser.readRow()
      doAssert parser.row == @["1", "2", "3"]
      ## Blank lines are skipped.
      doAssert parser.readRow()
      doAssert parser.row == @["10", "20", "30"]

      var emptySeq: seq[string]
      doAssert parser.readRow() == false
      doAssert parser.row == emptySeq
      doAssert parser.readRow() == false
      doAssert parser.row == emptySeq

      parser.close()
      strm.close()

  Source Edit

    proc rowEntry(self: var CsvParser; entry: string): var string {.
        ...raises: [KeyError], tags: [], forbids: [].}

  Accesses a specified `entry` from the current row.

  Assumes that readHeaderRow has already been called.

  If specified `entry` does not exist, raises KeyError.

  Example:

      import std/streams
      var strm = newStringStream("One,Two,Three\n1,2,3\n\n10,20,30")
      var parser: CsvParser
      parser.open(strm, "tmp.csv")
      ## Requires calling `readHeaderRow`.
      parser.readHeaderRow()
      doAssert parser.readRow()
      doAssert parser.rowEntry("One") == "1"
      doAssert parser.rowEntry("Two") == "2"
      doAssert parser.rowEntry("Three") == "3"
      doAssertRaises(KeyError):
        discard parser.rowEntry("NonexistentEntry")
      parser.close()
      strm.close()

  Source Edit