Removing an element from std:vector in Cython

Question

From Cython I'm using C++'s std:vector and I need to remove an element. For my exact use case all of the vectors are of type int. I thought that the cleanest way to do this would be to use std:remove and vector's erase method. For some reason the following code is not removing the elements as expected:

# distutils: language=c++
from libcpp.vector cimport vector
cdef extern from "<algorithm>" namespace "std":
     iter std_remove "std::remove" [iter, T](iter first, iter last, const T& val)

cdef void remove(vector[int] vect, int elem):
    vect.erase(std_remove[vector[int].iterator, int](vect.begin(), vect.end(), elem))

def blah():
    cdef vector[int] vect
    cdef int i
    for i in range(10):
        vect.push_back(i)
    for i in range(10):
        print vect[i]
        remove(vect, i)
    return vect

When I run print blah() I see:

0
1
...
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

In other words the elements are not being removed from the vector. What simple mistake am I making?

Answer 1

Removing an element from a vector in C++ is extremely easy. Your erase/remove combo is for more complicated stuff.

Given an iterator it, then

v.erase(it)

will erase it (see the pertinent vector doc).

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Incidentally, if you need to find this iterator, you can use find (from algorithm):

std::find(v.begin(), v.end(), value);

Consequently, to erase the first occurrence of value, you can use

v.erase(std::find(v.begin(), v.end(), value));

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P.S. This isn't really a Cython question at all. It's a C++ question which came up in the context of Cython. Please consider retagging. This will help you get attention for your question from relevant people.