Lua table sort does not work

Question

I have the below program code which tries to sort a given list. I have tried various options and it still doesn`t work.

local List = {}    
List[143] = "143"    
List[145] = "145"    
List[120] = "120"       
List[178] = "178"   
table.sort(List, compare)

compare function is defined as

function compare(a, b)    
    if tonumber(a) < tonumber(b) then    
        return true    
    end
end

Above table.sort does not work to any order. I just want to sort it to increasing numerical order. If you have any ideas about this please help me. Thanks in advance

Answer 1

table.sort (and much of the rest of the table.* functions) is defined only for operations on array-like tables. That means tables with contiguous integer keys from 1..n. Your table doesn't meet those criteria.

Answer 2

The keys of that table do not satisfy requirements of that function. The keys must start at 1 and sequentially increase to N, as per Lua ref manual ("Sorts table elements in a given order, in-place, from table[1] to table[n]"). Try

local List = {}
List[1] = "143"    
List[2] = "145"    
List[3] = "120"       
List[4] = "178"   
table.sort(List, compare)

or even better

local List = {"143", "145", "120", "178"}
table.sort(List, compare)