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Sorting a table by two columns?

 
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fmanager
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Joined: 17 Feb 2016
Posts: 431

PostPosted: Tue Mar 07, 2017 6:10 pm    Post subject: Sorting a table by two columns? Reply with quote

Say, if I have a table like this:
Code:

table = {
         type= "work", id = 5}
         type= "game", id = 2}
         type= "work", id = 3}


I want to first sort the table based on the "type", and then sort it on "id" from the biggest to the smallest value. The result should be like this:
Code:

table = {
         type= "work", id = 5}
         type= "work", id = 3}
         type= "game", id = 2}


The only way I can think of is to sort the table based on "type" first, then separate the table into two tables based on their "type", then sort them based on "id", at last, combine them into the final table...... But there must be a smarter way to do this. Sad

Thanks.

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panraven
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Joined: 01 Oct 2008
Posts: 626

PostPosted: Tue Mar 07, 2017 6:27 pm    Post subject: Reply with quote

Try use a sort with comparison that the secondary keys of two items are checked only if the primary keys of the two items are the same,eg.
Code:

-- fix syntax: 'table' is a build-in module, should not assign as global variable
mytable = {
         {type= "work", id = 5} ,
         {type= "game", id = 2} ,
         {type= "work", id = 3} ,
}
table.sort(mytable, function(a,b)
  if  a.type == b.type then return a.id < b.id else return a.type < b.type end
end)

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fmanager
Master Cheater
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Joined: 17 Feb 2016
Posts: 431

PostPosted: Tue Mar 07, 2017 6:54 pm    Post subject: Reply with quote

panraven wrote:
Try use a sort with comparison that the secondary keys of two items are checked only if the primary keys of the two items are the same,eg.
Code:

-- fix syntax: 'table' is a build-in module, should not assign as global variable
mytable = {
         {type= "work", id = 5} ,
         {type= "game", id = 2} ,
         {type= "work", id = 3} ,
}
table.sort(mytable, function(a,b)
  if  a.type == b.type then return a.id < b.id else return a.type < b.type end
end)


Thank you panraven, you helped me with sorting again. Very Happy

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