How to sort a table on multiple values in lua?

Question

I need a function sort_on_values(t, ...) where ... are the variables by which the table t should be sorted. or sort_on_values(t, t_v) where t_v is a table with variables by which the table t should be sorted. Or something like that.

Function returns sorted table or sorts existing one.

Example #1:

I have a table

t = {{a=1,b=2,c=3},
     {a=1,b=1,c=2},
     {a=3,b=2,c=2}}

I do this:

t = sort_on_values(t,a,b,c)

And as result I get:

t == {{a=1,b=1,c=2},
      {a=1,b=2,c=2},
      {a=3,b=2,c=2}}

Example #2:

I do this:

t = sort_on_values(t,b,a,c)

And as result I get:

t == {{a=1,b=1,c=2},
      {a=1,b=2,c=3},
      {a=3,b=2,c=2}}

This should also work if I have a table like

t = {{a=1,b=1,c=2,d=1},
     {a=1,b=2,c=3,d=2},
     {a=3,b=2,c=2,d=3}}

And so on.

How can I do that?

Egor Skriptunoff · Accepted Answer · 2017-07-18 15:52:56Z

4

Variant for vararg function

function sort_on_values(t,...)
  local a = {...}
  table.sort(t, function (u,v)
    for i = 1, #a do
      if u[a[i]] > v[a[i]] then return false end
      if u[a[i]] < v[a[i]] then return true end
    end
  end)
end

edited Jul 18, 2017 at 15:52

Egor Skriptunoff

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answered Jul 18, 2017 at 12:47

moteus

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Comments

lhf · Accepted Answer · 2017-07-18 11:16:28Z

1

Generic code for this task will probably take some work but you can start with this:

t = {
    {a=1,b=2,c=3},
    {a=1,b=1,c=2},
    {a=3,b=2,c=2},
}

function sort_on_values(t,a,b,c)
    table.sort(t, function (u,v)
        return
             u[a]<v[a] or
            (u[a]==v[a] and u[b]<v[b]) or
            (u[a]==v[a] and u[b]==v[b] and u[c]<v[c])
    end)
end

sort_on_values(t,"a","b","c")
for i=1,#t do
    print(i,t[i].a,t[i].b,t[i].c)
end

answered Jul 18, 2017 at 11:16

lhf

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1 Comment

me2 beats Over a year ago

Wow cool thanks! Seems to work. But what if I have "d", "e" etc? Ideally, I would like to have a more general solution. It seems more difficult to implement. But thanks anyway)

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