Convert string to numbers in Lua

Question

In Lua, I have a string like this: 231 523 402 1223 9043 -1 4 which contains several numbers separated by space. Now I would like to convert it into a vector of int numbers, how to achieve it with some built-in functions?

Answer 1

You can use string.gsub with a function as the replacement value.

If repl is a function, then this function is called every time a match occurs, with all captured substrings passed as arguments, in order.

An example of usage would look like this:

local function tovector(s)
    local t = {}
    s:gsub('%-?%d+', function(n) t[#t+1] = tonumber(n) end)
    return t
end

Using it is straight forward:

local t = tovector '231 523 402 1223 9043 -1 4'

The result is a vector (or sequence in Lua terminology):

for i,v in ipairs(t) do print(i,v) end

1       231
2       523
3       402
4       1223
5       9043
6       -1
7       4

Answer 2

Use tonumber to convert strings to numbers. Use string patterns to get the numbers from the string http://www.lua.org/manual/5.3/manual.html#pdf-string.gmatch

local example = "123 321 -2"
for strNumber in string.gmatch(example, "%-?%d+") do
  tonumber(strNumber)
end

%- will match a minus sign, while %-? will match minus sign optionally, in other words, there may be a minus.

%d+ will match any string segment that consists of one or more consequent digits.

Once you have your numbers you can insert them into a Lua table. http://www.lua.org/manual/5.3/manual.html#pdf-table.insert