check if the value already exists in vector - c++

Question

I have made a form that collects data which is then sent to a database.
Database has 2 tables, one is main and second one is in relation 1-to-many with it.
To make things clear, I will name them: main table is Table1, and child table is ElectricEnergy.
In table ElectricEnergy is stored energy consumption through months and year, so the table has following schema:
ElectricEnergy< #ElectricEnergy_pk, $Table1_pk, January,February, ...,December, Year>
In the form, user can enter data for a specific year. I will try to illustrate this bellow:
Year: 2012
January : 20.5 kW/h
February: 250.32 kW/h
and so on.
Filled table looks like this:
YEAR | January | February | ... | December | Table1_pk | ElectricEnergy_pk |
2012 | 20.5 | 250.32 | ... | 300.45 | 1 | 1 |
2013 | 10.5 | 50.32 | ... | 300 | 1 | 2 |
2012 | 50.5 | 150.32 | ... | 400.45 | 2 | 3 |
Since the number of years for which consumption can be stored is unknown, I have decided to use vector to store them.
Since vectors can’t contain arrays, and I need an array of 13 ( 12 months + year ), I have decided to store the form data into a vector.
Since data has decimals in it, vector type is double.
A small clarification:
vector<double> DataForSingleYear;
vector< vector<double> > CollectionOfYears.
I can successfully push data into vector DataForSingleYear, and I can successfully push all those years into vector CollectionOfYears.
The problem is that user can enter same year into edit box many times, add different values for monthly consumption, which would create duplicate values.
It would look something like this:
YEAR | January | February | ... | December | Table1_pk | ElectricEnergy_pk |
2012 | 20.5 | 250.32 | ... | 300.45 | 1 | 1 |
2012 | 2.5 | 50.32 | ... | 300 | 1 | 2(duplicate!) |
2013 | 10.5 | 50.32 | ... | 300 | 1 | 3 |
2012 | 50.5 | 150.32 | ... | 400.45 | 2 | 4 |
My question is:
What is the best solution to check if that value is in the vector ?
I know that question is “broad” one, but I could use at least an idea just to get me started.
NOTE:
Year is at the end of the vector, so its iterator position is 12.
The order of the data that will be inserted into database is NOT important, there are no sorting requirements whatsoever.
By browsing through SO archive, I have found suggestions for the usage of std::set, but its documentation says that elements can’t be modified when inserted, and that is unacceptable option for me.
On the other hand, std::find looks interesting.
( THIS PART WAS REMOVED WHEN I EDITED THE QUESTION:
, but does not handle last element, and year is at the end of the
vector. That can change, and I am willing to do that small adjustment if std::find can help me.
)
The only thing that crossed my mind was to loop through vectors, and see if the value already exists, but I don’t think it is the best solution:
wchar_t temp[50];
GetDlgItemText( hwnd, IDC_EDIT1, temp, 50 ); // get the year
double year = _wtof( temp ); // convert it to double,
// so I can push it to the end of the vector
bool exists = false; // indicates if the year is already in the vector
for( vector< vector <double> >::size_type i = 0;
i < CollectionOfYears.size(); i++ )
if( CollectionOfYears[ i ] [ ( vector<double>::size_type ) 12 ] == year )
{
exists = true;
break;
}
if( !exists)
// store main vector in the database
else
MessageBox( ... , L”Error”, ... );
I work on Windows XP, in MS Visual Studio, using C++ and pure Win32.
If additional code is needed, ask, I will post it.
Thank you.

Answer 1

Using find_if and lambda filter:
auto match = std::find_if(CollectionOfYears.begin(), CollectionOfYears.end(),
[&year](v){ return year == v.last(); })
if (match == CollectionOfYears.end()){ //no value previously
}
This still iterates the whole array. If you need more efficient search you should keep the array sorted and use binary search or std::set.
Note that vector::end() returns iterator to the element after the last element. This is why std::find ignores the last value (because it is already out of bounds!).