vermaxik

vermaxik

Hello Elixirforum,

Could you please explain how List Comparison works in Elixir?

Why such list of integers returns true

iex(15)> [3,10] > [3,3,3,3]
true

And the same example list of strings:

iex(16)> ["3","10"] > ["3", "3", "3", "3"]
false

I would expect in both examples false because of list size.

Thank you!

Showing Posts 1 to 5

NobbZ

NobbZ

List comparison works by comparing element by element.

For each pair of equal elements, the comparison advances to the next. The first that is not equal decides. And 10 is greater than 3 while "10" is not greater than "3".

You can learn more in the docs:

LostKobrakai

LostKobrakai

Lists are compared element by element, disregarding the size (tuples are compared by size then elements). So it should come down to integers and binaries comparing differently.

iex(1)> "10" > "3"
false
iex(2)> 10 > 3
true
vermaxik

vermaxik OP

Now it’s clear, thanks a lot @NobbZ and @LostKobrakai for your answers. :clap:

hauleth

hauleth

As for reasoning for this behaviour - computing size of list is as expensive as traversing whole list, so comparing two lists first by length and then by elements would make whole operation more expensive.

arbaz_asif

arbaz_asif

The most efficient way to compare two lists on the basis of their sizes is by using Enum.count() function from Enum Module. It will work like this:

Enum.count([3,10]) > Enum.count([3,3,3,3])
false

Enum.count(["3","10"]) > Enum.count(["3", "3", "3", "3"])
false
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