Difference between using "for i,v in pairs() do" and "for i, v, in next, table do"?

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#1

You can write your topic however you want, but you need to answer these questions:

  1. What do you want to achieve? Keep it simple and clear!
    What is the difference between using:
for i, v in pairs(table) do

end

and

for i, v in next, table do

end

  1. What is the issue? Include screenshots / videos if possible!
    Which one should I use and which one is more efficient?

  2. What solutions have you tried so far? Did you look for solutions on the Developer Hub?

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#3

tl;dr They’re exactly the same. pairs is just a convenience function which returns the next function:

function pairs (t)
  return next, t, nil
end

More info:

For loops are slightly more complicated in general. You can read some deep details here: Programming in Lua : 7 (it talks about pairs vs next in section 7.3).

I’ll try to summarize:

next is a function that, given a table and some key, returns another key, value pair in some arbitrary order. If you give it a nil key, it gives you the first in the order. If it returns nil, it’s done.

For example:

local t = {[4]="d", [3]="c", [2]="b", [1]="a"}

local k, v = nil, nil

k, v = next(t, k)
print(k, v) -- 3, c

k, v = next(t, k)
print(k, v) -- 2, b

k, v = next(t, k)
print(k, v) -- 4, d

k, v = next(t, k)
print(k, v) -- 1, a

k, v = next(t, k)
print(k, v) -- nil, nil

Your for loop just does i, v = next(table, i) over and over (starting with i=nil) until next returns nil.

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#4

There is no difference.
This is the same thing as pairs.

local function pairs(table)
    return next, table
end

However:
This is the sort of thing you should search instead of posting. It’s not just a rule, but it can bother the frequent people here. It’s been answered a few dozen times already in far better ways than I can hope to answer.

2 Likes