[MunkDev]

for i=1, #mydata do
    local value = mydata[i]
    -- do something with value in sequential array
end
 
for i, value in ipairs(mydata) do
    -- do something with value in sequential array
end
 
for i, value in pairs(mydata) do
    -- do something with value in associative array
end
 
mydata[#mydata + 1] = newValue -- append sequential
mydata["index"] = newValue -- insert associative
mydata[5] = newValue -- insert associative
 
table.insert(mydata, 1, newValue) -- prepend (put newValue at mydata[1])
table.insert(mydata, newValue) -- append (put newValue at mydata[#mydata + 1])

To explain what pairs and ipairs do, they essentially just return an index key and value associated with that key in pairs.

-- pairs, literally just a wrapper of std next
function pairs (t)
    return next, t, nil
end
 
-- ipairs, does an incremental lookup and stops when the value is nil
local function iter (a, i)
    i = i + 1
    local v = a[i]
    if v then
        return i, v
    end
end
 
function ipairs (a)
    return iter, a, 0
end

When to use pairs/ipairs?

• pairs - associative arrays, keys are non-numerical or not in sequence starting at 1.
• ipairs - numerically indexed arrays where there are no gaps between [1] and however many elements the table has.