What does "for i, v in ipairs do" mean?

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LaserGuns
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What does "for i, v in ipairs do" mean?

Post by LaserGuns »

I don't think that's exactly how its used, but I see "for blah blah in ipairs do" in a lot of code and I think it would be useful.
What does the for/do loop do?
What are ipairs? How do they work?
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Roland_Yonaba
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Re: What does "for i, v in ipairs do" mean?

Post by Roland_Yonaba »

Sometimes, for some reasons, you need to loop trhough a collection of elements.
For loop is meant for that purpose.

Code: Select all

t = { 'a','b','c','d'}
for i = 1, #t do 
   print(i,t[i])
end
will output
1, 'a'
2, 'b'
3, 'c'
4, 'd'
pairs/ipairs are iterators.
They offers better support to loop trough a table.

Code: Select all

t = { 'a','b','c','d'}
for key,value in ipairs(t) do 
   print(key,value)
end
will have the same output as before.
Pairs will also act the same way, and have the same output.

Sometimes, values are not indexed with numeric keys, in a table.
In this case, ipairs won't work, but pairs will.

Code: Select all

t = {}
t.x = 1
t.y = 2
t.z = 3
for key,value in pairs(t) do 
   print(key,value)
end
will output
"x",1
"y",2
"z",3
That's a basic example. You will find more intel here :
Lua_Tables_Tutorial
Pairs/ipairs

There's an online interpreter for Lua here, you can try some snippets there to understand.
Last edited by Roland_Yonaba on Sun Aug 19, 2012 1:45 am, edited 2 times in total.
LaserGuns
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Posts: 33
Joined: Sun Apr 29, 2012 12:55 am

Re: What does "for i, v in ipairs do" mean?

Post by LaserGuns »

Alright. Thanks!
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