# Calculate the intersection of two waves

The function below can be used to calculate the intersection of 2 one-dimensional integer waves, such as would be returned by the `Extract` operation using the `/INDX` flag. The intersection is stored in the resultWave parameter to the function. This wave must exist but will be redimensioned by the function as appropriate.

### Example:

``` Make/O/N=5 wave1, wave2, wave3 wave1= {1, 2, 3, 4, 5} wave2 = {3, 4, 5, 6, 7} CalculateWaveIntersection(wave1, wave2, wave3) print wave3 wave3= {3,4,5} ```

Suggestions for improvements to this function are welcome.

//**
// Calculates the intersection of two 1D integer waves.  You might use this to determine
// common indices in two destWaves created by the Extract/INDX operation.
//
// @param wave1
//  First 1D integer wave.
// @param wave2
//  Second 1D integer wave.
// @param resultWave
//  A wave where the result will be stored.  This wave will be overwritten if it already contains
//  any data.  The function will change the this to an integer wave if it is not already.
//*
Function CalculateWaveIntersection(wave1, wave2, resultWave)
WAVE wave1
WAVE wave2
WAVE resultWave

Variable wave1Rows = DimSize(wave1, 0)
Variable wave2Rows = DimSize(wave2, 0)
Variable longRows, shortRows
if (wave1Rows > wave2Rows)
Duplicate/O wave1, longWave
WAVE shortWave = wave2
longRows = wave1Rows
shortRows = wave2Rows
else
Duplicate/O wave2, longWave
WAVE shortWave = wave1
longRows = wave2Rows
shortRows = wave1Rows
endif

// Sort values in longWave
Sort longWave, longWave
Redimension/I/N=(0) resultWave

Variable n, numOutRows, longWaveRow
For (n=0; n<shortRows; n+=1)
longWaveRow = BinarySearch(longWave, shortWave[n])
if ((longWaveRow) >= 0 && longWave[longWaveRow] == shortWave[n])
Redimension/N=(numOutRows + 1) resultWave
resultWave[numOutRows] = shortWave[n]
numOutRows += 1
endif
EndFor
KillWaves/Z longWave
End Forum Support Gallery