For duplicates an array formula
Rich (BB code):
=SUM(SIGN(COUNTIF(A1:A10,B1:B10)))
should be more suitable... Best regards.
The OP wants a count of the items from B1:B10 which match A1:A10.
That is, target range = B1:B10, criteria range = A1:A10.
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The formula...
[1]
Rich (BB code):
{=SUM(SIGN(COUNTIF(B1:B10,A1:A10)))}
would be affected by the duplicates that are in the criteria range while occurring just once in the target range...
Here it yields 4.
So would...
[2]
Rich (BB code):
{=SUM(COUNTIF(B1:B10,A1:A10))}
[3]
Rich (BB code):
=SUMPRODUCT(COUNTIF(B1:B10,A1:A10))
But...
[4]
Rich (BB code):
=SUMPRODUCT(ISNUMBER(MATCH(B1:B10,A1:A10,0))+0)
returns a count of 3.
If the intent is to return the count of unique matching items, we would need something like:
[5]
Rich (BB code):
{=SUM(IF(FREQUENCY(IF(ISNUMBER(MATCH(B1:B10,A1:A10,0)),
MATCH(B1:B10,A1:A10,0)),ROW(B1:B10)-ROW(B1)+1),1))}
Note. Formulas with { and } around are array (CSE) formulas.