Count unique number of elements based on another cell range

Question

I have two columns in my Excel sheet. Column A contains Wk No , Column B Dates :

Wk. No    Dates  
1228      9-Jul  
1228      10-Jul  
1228      11-Jul  
1228      11-Jul  
1228      12-Jul  
1228      13-Jul  
1229      16-Jul  
1229      16-Jul  
1229      17-Jul

I want the following result:

Wk. No    No-of-days  
1228       5  
1229       2

How to get this in Excel? I can get the number of unique days but cannot control the formula to calculate unique days based on the week number.

Answer 1

You can use

COUNTIF(RANGE,CRITERIA)

Like

Wk.No          No-of-days
1228           =COUNTIF(RANGE,<Cell Reference of 1228>)
1229           =COUNTIF(RANGE,<Cell Reference of 1229>)

Answer 2

If Wk. No Wk. No is in A1 and 1228 and 1229 in C2 and C3, respectively, then:

=SUM(IF(A2:A10=C2,1/(COUNTIFS(A2:A10,C2,B2:B10,B2:B10)),0))  

entered with Ctrl + Shift + Enter and copied down one row should suit. Courtesy of Get Digital Help where a full explanation is available.

Of course would be much easier with Excel 2013.