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Lua-CSV - delimited file reading

1. What?

Lua-CSV is a Lua module for reading delimited text files (popularly CSV and tab-separated files, but you can specify the separator).

Lua-CSV tries to auto-detect whether a file is delimited with commas or tabs, copes with non-native newlines, survives newlines and quotes inside quoted fields and offers an iterator interface so it can handle large files.

2. How?

local csv = require("csv")
local f ="file.csv")
for fields in f:lines() do
  for i, v in ipairs(fields) do print(i, v) end
end takes a second argument parameters, a table of parameters controlling how the file is read:

  • separator sets the separator. It'll probably guess the separator correctly if it's a comma or a tab (unless, say, the first field in a tab-delimited file contains a comma), but if you want something else you'll have to set this. It could be more than one character, but it's used as part of a set: "["..sep.."\n\r]"

  • Set header to true if the file contains a header and each set of fields will be keyed by the names in the header rather than by integer index.

  • columns provides a mechanism for column remapping. Suppose you have a csv file as follows:


    And columns is:

    • { word = true } then the only field in the file would be { word = "ONE" }

    • { first = { name = "word"} } then it would be { first = "ONE" }

    • { word = { transform = string.lower }} would give { word = "one" }

    • finally,

        { word = true
          number = { transform = function(x) return tonumber(x) / 10 end }}

      would give { word = "ONE", number = 1 }

    A column can have more than one name: { first = { names = {"word", "worm"}}} to help cope with badly specified file formats and spelling mistakes.

  • buffer_size controls the size of the blocks the file is read in. The default is 1MB. It used to be 4096 bytes which is what pagesize says on my system, but that seems kind of small.

csv.openstring works exactly like except the first argument is the contents of the csv file. In this case buffer_size is set to the length of the string.

3. Requirements

Lua 5.1, 5.2 or LuaJIT.

4. Issues

  • Some whitespace-delimited files might use more than one space between fields, for example if the columns are "manually" aligned:

      street           nr  city
      "Oneway Street"   1  Toontown

    It won't cope with this - you'll get lots of extra empty fields.

5. Wishlist

  • Tests would be nice.
  • So would better LDoc documentation.

6. Alternatives

  • Penlight contains delimited file reading. It reads the whole file in one go.
  • The Lua Wiki contains two pages on CSV here and here.
  • There's an example using LPeg to parse CSV here