Cookbooks
Lua
Chapter 10. Data Formats and Serialization
Working with CSV

Lua:
Working with CSV

How to:

In Lua, working with CSV files can be approached using basic file IO operations provided by the language, without the need for external libraries for simple tasks. For more complex operations, such as handling special cases (e.g., commas within values), it might be beneficial to use third-party libraries like lua-csv.

Reading a CSV file

Here’s a simple example to read a CSV file line by line, splitting each line into values based on the comma separator.

function parseCSVLine(line)
    local result = {}
    local from = 1
    local sep = ","
    local field
    while true do
        local start, finish = string.find(line, sep, from)
        if not start then
            table.insert(result, string.sub(line, from))
            break
        end
        field = string.sub(line, from, start - 1)
        table.insert(result, field)
        from = finish + 1
    end
    return result
end

local file = io.open("example.csv", "r")
for line in file:lines() do
    local values = parseCSVLine(line)
    for i, v in ipairs(values) do
        print(i, v)
    end
end
file:close()

Sample output (for an example.csv with content “name,age\newlineJohn Doe,30\newlineJane Doe,32”):

1	name
2	age
1	John Doe
2	30
1	Jane Doe
2	32

Writing a CSV file

To generate a CSV file, you simply construct strings with comma-separated values and write them to a file line by line.

local data = {
    {"name", "age"},
    {"John Doe", "30"},
    {"Jane Doe", "32"}
}

local file = io.open("output.csv", "w")
for _, v in ipairs(data) do
    file:write(table.concat(v, ","), "\n")
end
file:close()

This would create (or overwrite) an output.csv file with the specified data.

Using lua-csv

For more advanced CSV handling, including support for quotes and escape characters, the lua-csv library is a robust choice.

First, install it using LuaRocks:

luarocks install lua-csv

Then, reading a CSV file becomes as simple as:

local csv = require("csv")

-- Reading from a file
for fields in csv.open("example.csv") do
    for i, v in ipairs(fields) do
        print(i, v)
    end
end

And writing to a CSV with proper quoting and escaping:

local file = csv.open("output.csv", {write=true})

local data = {
    {"name", "profession", "location"},
    {"John Doe", "Software Engineer", "New York, NY"},
    {"Jane Doe", "Data Scientist", "\"San Francisco, CA\""}
}

for _, v in ipairs(data) do
    file:write(v)
end

This approach automatically handles complexities such as commas and quotes within values.

Working with JSON