Combination Functions – Combina()

Combin and Combina Functions

The Excel Combin and CombinA functions both calculate a number of combinations of a set of objects.
However, the two functions differ in that the Combin function does not count repetitions whereas the CombinA function does count repetitions.
For example, in a set of 3 objects, a, b, c, how many combinations of 2 objects are there?
The Combin function returns the result 3 (combinations: ab, ac, bc);
The Combina function returns the result 6 (combinations: aa, ab, ac, bb, bc, cc).

CombinA() Function

The Excel Combina function calculates the number of combinations, with repetitions, of a given number objects from a set.


Syntax

The syntax for the COMBINA function in Microsoft Excel is:

=COMBINA( number, chosen )

Parameters or Arguments

number

The number of items represented as an integer. It can not be a negative value and it must be greater than or equal to chosen. If a non-integer value is entered for this parameter, it will truncate the value.

chosen

The number of items in a combination. It can not be a negative value. If a non-integer value is entered for this parameter, it will truncate the value.

Excel Combina Function Examples

For any 6 objects (e.g. a, b, c, d, e, f), there are 21 different combinations (with repetitions) of 2 objects. These are:

aa
ab
ac
ad
ae
af
bb
bc
bd
be
bf
cc
cd
ce
cf
dd
de
df
ee
ef
ff

This calculation is shown in cell A2 of the following example spreadsheet.
The example spreadsheet below also shows the Combina function used to calculate the number of combinations (with repetitions) for other numbers of objects taken from a set of 6.

Formulas:


A
1
=COMBINA( 6, 1 )
2
=COMBINA( 6, 2 )
3
=COMBINA( 6, 3 )
4
=COMBINA( 6, 4 )
5
=COMBINA( 6, 5 )
6
=COMBINA( 6, 6 )

Results:


A
1
6
2
21
3
56
4
126
5
252
6
462

Notes

   The COMBINA function was only introduced in Excel 2013 and so is not available in earlier versions of Excel.
   Arguments that contain decimal values are truncated to integers.
   COMBINA returns a #VALUE! error value if either argument is not numeric.
   If number is less than number chosen, COMBINA returns #NUM!

References

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