Lua - convert a table into a comma separated list

Question

I need to convert a table into a comma separated list in order to save it to a text file. Is there a built in method for doing this in Lua?

Solution 1

There isn't a built in function, but there are examples onthe web.

This is a decent one actually.

Solution 2

If your table is an array, you can use table.concat to print CSVs:

t={10,20,30}
print(table.concat(t,","))

outputs 10,20,30.

Solution 3

No, there is not a "built in" function for this. But it's not hard to do it yourself. I keep a script around for recursively writing Lua tables directly to files as Lua scripts, which can then be loaded and executed like Lua scripts.

--This file exports a function, WriteTable, that writes a given table out to a given file handle.

local writeKey = {};

function writeKey.string(hFile, value, iRecursion)
    WriteFormatted(hFile, "[\"%s\"]", value);
end

function writeKey.number(hFile, value, iRecursion)
    WriteFormatted(hFile, "[%i]", value);
end

local writeValue = {};

function writeValue.string(hFile, value, iRecursion)
    WriteFormatted(hFile, "[==[%s]==]", value);
end

function writeValue.number(hFile, value, iRecursion)
    WriteFormatted(hFile, "%i", value);
end

function writeValue.boolean(hFile, value, iRecursion)
    if(value) then hFile:write("true"); else hFile:write("false"); end;
end

function writeValue.table(hFile, value, iRecursion)
    WriteTable(hFile, value, iRecursion)
end

local function WriteFormatted(hFile, strFormat, ...)
    hFile:write(string.format(strFormat, ...));
end

local function WriteForm(hFile, strFormat, ...)
    hFile:write(string.format(strFormat, ...));
end

local function WriteTabs(hFile, iRecursion)
    for iCount = 1, iRecursion, 1 do
        hFile:write("\t");
    end
end

function WriteTable(hFile, outTable, iRecursion)
    if(iRecursion == nil) then iRecursion = 1; end

    hFile:write("{\n");

    local bHasArray = false;
    local arraySize = 0;

    if(#outTable > 0) then bHasArray = true; arraySize = #outTable; end;

    for key, value in pairs(outTable) do
        if(writeKey[type(key)] == nil) then print("Malformed table key."); return; end
        if(writeValue[type(value)] == nil) then
            print( string.format("Bad value in table: key: '%s' value type '%s'.", key, type(value)));
            return;
        end

        --If the key is not an array index, process it.
        if((not bHasArray) or
                (type(key) ~= "number") or
                not((1 <= key) and (key <= arraySize))) then
            WriteTabs(hFile, iRecursion);
            writeKey[type(key)](hFile, key, iRecursion + 1);
            hFile:write(" = ");
            writeValue[type(value)](hFile, value, iRecursion + 1);

            hFile:write(",\n");
        end
    end

    if(bHasArray) then
        for i, value in ipairs(outTable) do
            WriteTabs(hFile, iRecursion);
            writeValue[type(value)](hFile, value, iRecursion + 1);
            hFile:write(",\n");
        end
    end

    WriteTabs(hFile, iRecursion - 1);
    hFile:write("}");
end

Comments

[clua7]

what is the underscore used for here? Haven't seen this before: for _,p in pairs(tt) do s = s .. "," .. escapeCSV(p) end

[Alan]

since pairs(table) returns a the key and value, the _ indicates you don't care about the key.

[Hack-R]

Please put the full answer in the answer itself instead of only linking to an external resource.