Anybody know how pairs work?

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#1

For iterative table , like {thing1,thing2} i know how it work and why ipairs is way better but i don’t get how pairs work the only way i can think about it , is that pairs search for every index combinaison but this would require a insane amount of iteration and would be way too laggy so i wonder if anybody know how it really work

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#3

Honestly, I don’t understand the difference. I was taught to use pairs but I’d like to know how ipairs and pairs differ as well.

#4

pairs basically loops through a table, ipairs does the same purpose of pairs but does it in order and is faster but slower in vanilla Lua.

#5

ipairs can only be use on list like {thing1,thing2} and not dictionary {thing1 = thing1b,thing2 = thing2b} because the i of ipairs is for index , it work with a code like that :

local i = 1
while table[i] do 
 --Action
i+=1 
end

So it require a continue index but it’s way faster

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#6

Okay, but why is it faster ? :thinking:

#8

Idk lol. Maybe because it runs an iterator? Idk.

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#9

Yeah but the question was how it can loop through a dictionary

#10

I’m not exactly sure how it works. Maybe it keeps a list of the keys in a table and iterates through that, accessing the value in the dictionary every time it gets another key? I don’t really know :thinking:.

#11

Interesting , so that would explain why lua start index to 1 since 0 is reserve to key list to do something like that

for i,v in ipairs(table[0]) do
 yield v,table[v]
end

(i use yield as in python , a return that don’t stop the program idk if this work in lua)

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#12

I think ipairs is faster because the programs only understand numbers, and since pairs can use keys with letters, it must transform the other characters to numbers, it takes slightly a little longer for the conversion.

PS: this post should be in #help-and-feedback:scripting-support

#13

Indeed i’ll change that

PS: this post should be in #help-and-feedback:scripting-support

#14

Smart, because computers are good at numbers while pairs can also be used in string dictionaries.

#16

This page should be a good way to see how ipairs and pairs works internally.

https://www.lua.org/pil/7.3.html

From what I see, ipairs is a simple loop that keeps adding and indexing, until the returned value becomes nil.

Now with pairs it does the same but instead of doing i += 1 it does i = next(t, i).

Next is a built in function that returns the next index and value in a dictionary.

next(t) on its own would return the first index in the dictionary, and then you use that one as the i arguement again.

for i,v in next, {['key'] = 'value'} ==  for i, v in pairs({['key'] = 'value'}