Collection library

[mjcoon]

Originally Posted by agraham

Haven't got time to look at "next" at the moment but

If index < 0 then
    index = 1 - index ' complement
End If

Thanks again; that was my conclusion too! But I was not negating or complementing the result. Merely testing for " > -1" which should have trapped all mismatches but didn't.

Please ignore my winge about IndexOf(); that problem was down to my not noticing that the order of arguments is quite different from BinarySearch()

[agraham]

Sorry, the perils of haste , dinner was ready to serve! The above is wrong, it should be

If index < 0 then
    index = 0 - 1 - index ' complement
End If

so
0xffff (-1) => 0
0xfffe (-2) => 1
0cfffd (-3) => 2
etc.

[mjcoon]

Originally Posted by agraham

Sorry, the perils of haste , dinner was ready to serve! The above is wrong, it should be

If index < 0 then
    index = 0 - 1 - index ' complement
End If

so
0xffff (-1) => 0
0xfffe (-2) => 1
0cfffd (-3) => 2
etc.

Thanks again Andrew. It would be nice to have this explained in the Help, but maybe it is not worth doing that now it is enshrined in this relevant thread.

None of the above explains why I am getting zero returned from BinarySearch() whereas IndexOf() gives the results I expect and works fine. The demo program works OK if tweaked to look for missing values. BTW I think that the constants are singular as in the Help, not cNumbers. I suppose if you have the detection suppressed this means you will get a null string or zero passed to the operation instead of the intended constant, which could give strange results.

My look-up arrays are generated by sparsely storing a counter, so are sorted numerically from the outset; I do not perform a sort operation. If you wanted(?) to investigate I could write out a sample array. (It is derived from zooming an OS-GB vector road-map.)

Mike.

[agraham]

Time dims the memory. All is now clear! Unfortunately there is a bug in ArraysEx.BinarySearch and ArrayListEx.BinarySearch. The .NET documentation is correct but in attempting to make this statement in the help true

If value is not found a negative number is returned. If the absolute value of this number is greater than or equal to the size of the array, there are no elements larger than value in the array. Otherwise, it is the index of the first element that is larger than value.

and notionally make things simpler by compensating for the bitwise inversion I missed that zero would be rturned both for a match at index 0 and for a no match when all the elements are larger than the search value. So as you suggested earlier a zero return is ambiguous and needs a further check doing to be correctly interpreted.