is there std::mismatch for two unequal sized vectors?

Question

I d like to compare two vectors where the second one might have more/less items than the first one.

v1 = 1,2,3,4,5

v2 = 1,0,3,4,5,6

As far as I understood, std::mismatch woNT do the trick. How could I detect the missing element in the v1?

Thanks in advance,

Orkun

Have you tried set_difference? http://www.cplusplus.com/reference/algorithm/set_difference/ — Trenin, Jan 22 '14 at 16:12

score 3 · Accepted Answer · answered Jan 22 '14 at 16:16

3

C++14 adds two additional overloads that accommodate different sized ranges

template< class InputIt1, class InputIt2 >
std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,
              InputIt2 first2, InputIt2 last2 );

template< class InputIt1, class InputIt2, class BinaryPredicate >
std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,
              InputIt2 first2, InputIt2 last2,
              BinaryPredicate p );

You might be able to use these by setting -std=c++1y on gcc and clang

answered Jan 22 '14 at 16:16

Praetorian

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C++14 support might be a bit optimistic at the moment! – Sean Jan 22 '14 at 16:43
2

@Sean Indeed, libstdc++ [doesn't](http://coliru.stacked-crooked.com/a/894d25237202ccdf) contain those overloads, but looking at the latest libc++ [source](http://llvm.org/svn/llvm-project/libcxx/trunk/include/algorithm) I can find both of them. So clang + libc++ might be an option. Edit: The latest libstdc++ [source](http://repo.or.cz/w/official-gcc.git/blob/HEAD:/libstdc%2B%2B-v3/include/bits/stl_algobase.h#l1334) includes them too. – Praetorian Jan 22 '14 at 16:50

score 1 · Answer 2 · edited May 23 '17 at 12:07

Use set_symmetric_difference(), but before this the source ranges must be ordered:

vector<int> v1;
vector<int> v2;

// ... Populate v1 and v2

// For the set_symmetric_difference algorithm to work, 
// the source ranges must be ordered!    
vector<int> sortedV1(v1);
vector<int> sortedV2(v2);

sort(sortedV1.begin(),sortedV1.end());
sort(sortedV2.begin(),sortedV2.end());

// Now that we have sorted ranges (i.e., containers), find the differences    
vector<int> vDifferences;

set_symmetric_difference(
    sortedV1.begin(), sortedV1.end(),
    sortedV2.begin(), sortedV2.end(),
    back_inserter(vDifferences));

After this, all different elements of these two vectors (i.e. either in v1 or v2, but not both) will be stored in vector<int> vDifferences. For your example, it will be {0, 2, 6}.

[...] Computes symmetric difference of two sorted ranges: the elements that are found in either of the ranges, but not in both of them are copied to the range beginning at d_first. The resulting range is also sorted. [...]

If you just need the missing elements in the v1, you can further scan this vDifferences against sortedV1 to find them out.

Check out this discussion for more info.

is there std::mismatch for two unequal sized vectors?

2 Answers2