Imported From: https://issues.scala-lang.org/browse/SI-9877?orig=1
Reporter: Josenildo SIlva (josenildo.silva)
Affected Versions: 2.11.8

@SethTisue said:
why erroneous? it appears to me the answers satisfy the definitions of multiset difference and intersection given in the Scaladoc for these methods.

Josenildo SIlva (josenildo.silva) said:
You have tested the sample sended. When exists repetitions and exists variance between characters the response is incorrect. I do not understand as that is correct.

@SethTisue said:
Let's take "intersect" for example. The Scaladoc for "intersect" says:

• If an element value x appears ''n'' times in that, then the first ''n'' occurrences of x will be retained in the result, but any following occurrences will be omitted.

Consider "SOSSSSSSSSSSSSO" intersect "SOSSOSSOSSOSSOS" and the letter O. O occurs at least twice on the right, so both O's on the left should be retained. You're telling me the answer ought to be "SOSSSSSSSS", but that only has one O in it.

Josenildo SIlva (josenildo.silva) said:
Exists one simple confusing here. If intersection compare each item in same position in each String so only one 'O' have to be returned no more. I will be test that in Java and C++ and Python. I will be comparing results. If I get same result that Scala close that question If not exists some erroneous interpretation mine. Thank for while but please not close that at tests.

Josenildo SIlva (josenildo.silva) said:
Okay. As I speaks it's incorrect. View that:

#include
#include
#include
#include
#include

using namespace std;

int main()
{
string a = "SOSSSSSSSSSSSSO";
string b = "SOSSOSSOSSOSSOS";
string c;

set_intersection(
    a.begin(), a.end(),
    b.begin(), b.end(),
    back_inserter(c));

cout << c << '\n';

}

Response:
Success time: 0 memory: 3460 signal:0
SOSSSSSSSSS

@SethTisue said:
it appears to me from a quick glance at http://www.cplusplus.com/reference/algorithm/set_intersection/ that the STL's set_intersection method implements set intersection on sorted ranges. Scala's intersection method, on the other hand, implements multiset intersection and doesn't require sorted input. So you shouldn't expect the same answer.

Josenildo SIlva (josenildo.silva) said:
No. This is not sorted in entry. If sorted in entry okay, But the entry is not sorted. I can search others implementations in Java and Python and Haskell. Let's go compare all that platforms.

@SethTisue said:

~ % ghci
GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
Prelude> import Data.List
Prelude Data.List> intersect "SOSSSSSSSSSSSSO" "SOSSOSSOSSOSSOS"
"SOSSSSSSSSSSSSO"

I think our methods are working as designed and documented. If you think they ought to be designed differently, I'd suggest that you start a mailing list thread about it and see if there is consensus. (But personally I think you'd have an uphill battle there.)

@SethTisue said:
And/or, you might (via pull request) would suggest improvements to the documentation, if you think it isn't sufficiently explicit and clear.

Josenildo SIlva (josenildo.silva) said:
Not need only for that case I'm use C++ not Scala. or Haskell because for that case I do not sort elements I send that unordered elements and need positional response each position is equal intersect not equal not return with not is equal in determined position.
In case where need search for new proteins or series of proteins you can'nt ordered the protein you have get positional similarity for one serie. This is because I had thinking that is one issue. But is the language is designed that form and is your specification not need change any information.

@SethTisue said:
I'm guessing, but perhaps this will be helpful for your use case?

scala> ("SOSSSSSSSSSSSSO" zip "SOSSOSSOSSOSSOS").count{case (a, b) => a != b}
res12: Int = 5

Josenildo SIlva (josenildo.silva) said:
Sorry, but, If you have series with 10^100(power) characters it's not efficient the problem here is performance and if you get one more direct access without any type of combination is more efficient. Thank you for your attention and help. I will be resolve that with other form. Thank you for all.