CODEWITHSUNDEEP
c++vector
user3251195
user3251195

Reputation: 17

Correctly erasing an element from a vector

If I have a table of vectors declared as

vector<int> table[9][9] and I want to compare and delete the element if it already exists, would the deletion be:

for(int row = 0; row < 9; row++)//erases the current choice from the whole row
 {
   for(int h = 0; h < (int)table[row][k].size();h++)
   {
     if(table[row][k][h] == table[i][k][0])
     {
       table[row][k].erase(table[row][k].begin() + h);
      }
    }
  }

I thought this would work, but I'm not 100% because I tried to delete every element using this technique and it didn't work, for those of you who want to see the code I used to delete all the elements, then it is:

for(int i = 0; i < 9; i++)
for(int k = 0; k < 9; k++)
      for(int n = 0; n < table[i][k].size();n++)
        table[i][k].erase(table[i][k].begin + n);

this method did not work, so I used clear instead.

Upvotes: 0

Views: 107

Answers (1)

Steve Jessop
Steve Jessop

Reputation: 279195

I don't know what choice and k are, but to erase all values from a vector v that are equal to a particular value val use the "erase-remove idiom":

v.erase(
    std::remove(v.begin(), v.end(), val),
    v.end()
);

Hence, to do this same thing for all vectors in table:

for (auto &row : table) {
    for (auto &v : row) {
        v.erase(
            std::remove(v.begin(), v.end(), val),
            v.end()
        );
    }
}

If you have a more complicated condition than equality, use remove_if in place of remove. But in your case, the extra condition involving puzzle doesn't use the loop variable h, so I think you can test that before looking in the vector:

if (puzzle[row][k] == 0) {
    // stuff with erase
}

In C++03 you can't use "range-based for loops" for (auto &row : table). So if you don't have C++11, or if you need the index for use in the puzzle test, then stick with for(int i = 0; i < 9; i++).

Upvotes: 4

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