Lua sorting values of tables within table

Question

I am very new to Lua, so please be gentle.

I want a sorted results based on the "error" key. For this example, the output should be:

Here is my script:

records = {}

records["a"] = {["count"] = 10, ["error"] = 20}
records["b"] = {["count"] = 30, ["error"] = 40}
records["c"] = {["count"] = 50, ["error"] = 70}
records["d"] = {["count"] = 25, ["error"] = 50}

function spairs(t, order)
    -- collect the keys
    local keys = {}
    for k in pairs(t) do keys[#keys+1] = k end

    -- if order function given, sort by it by passing the table and keys a, b,
    -- otherwise just sort the keys
    if order then
        table.sort(keys, function(a,b) return order(t, a, b) end)
    else
        table.sort(keys)
    end

    -- return the iterator function
    local i = 0
    return function()
        i = i + 1
        if keys[i] then
            return keys[i], t[keys[i]]
        end
    end
end

for k, v in pairs(records) do
    for m, n in pairs(v) do
        for x, y in spairs(v, function(t,a,b) return t[b] < t[a] end) do
            line = string.format("%s %5s   %-10d", k, n, y)
        end
    end
    print(line)

end

I found this about sorting a table and tried to implement it. But it does not work, results are not sorted.

hjpotter92 · Accepted Answer · 2014-11-17 20:47:19Z

1

table.sort only works when the table elements are integrally indexed. In your case; when you try to call spairs, you are actually calling table.sort on the count and error indices.

First off; remove the ugly, irrelevant nested for..pairs loops. You only need the spairs for your task.

for x, y in spairs(records, function(t, a, b) return t[b].error < t[a].error end) do
    print( x, y.count, y.error)
end

And that is all.

answered Nov 17, 2014 at 20:47

hjpotter92

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