[erlang-questions] Question about ETS documentation

Soup zachary.hueras@REDACTED
Mon Mar 31 05:14:30 CEST 2014

Pos refers to a position in the stored tuple. ets:lookup_element returns
only one of the values from the tuple, as opposed to ets:lookup which
returns the tuple in its entirety (in a list for compatibility with
bag-type tables).

One reason you might prefer lookup_element as opposed to lookup is that
it's slightly cheaper to copy from the table (as you're not copying as much
data), but it's also generally useful as a shorthand for retrieving one
piece of the stored tuple so you don't have to bind the entire return value.

If I recall correctly, lookup_element, update_element, and update_counter
only work with tables of type set or ordered_set.


On Sun, Mar 30, 2014 at 6:45 PM, Yves S. Garret

> Hello,
> I've been reading this documentation:
> http://www.erlang.org/doc/man/ets.html#lookup_element-3
> What I have a hard time figuring out is what the Pos means.  Why would it
> be needed at all?  I'm looking at this code:
> ...
> Cx_PId = ets:lookup_element(IdsNPIds, Cx#cortex.id, 2),
> ...
> And I have no idea what this and why have it there.  I've already
> specified the element that we're searching for, why the position?  Does the
> position refer to the element that's located inside of the return value?
> As in, I want the 2nd element from the return value?
> Thanks in advance.
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> erlang-questions mailing list
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