preventing duplication

lezawang

Well-known Member
Joined
Mar 27, 2016
Messages
1,805
Office Version
  1. 2016
Platform
  1. Windows
Hi
I know the formula to use to prevent duplication, thanks for your help. So I went to Data Validation->custome then wrote this formula

= countif($a1:$a5,a1)=1

but did not fully understand it

here is my understanding

This formula will be apply on all the range

=countif(range,a1) =1
=countif(range,a2) =1
=countif(range,a3) =1
=countif(range,a4) =1
=countif(range,a5) =1

let say i want to enter 100 in cell a4, so the formula is =countif(range,a4)=1, so this formula is true because I have a1= 100 therefore excel wont accept me to enter that value. Am I right?

100
200
300

<tbody>
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Excel Facts

Repeat Last Command
Pressing F4 adds dollar signs when editing a formula. When not editing, F4 repeats last command.
You have the main idea. However, that formula only works on A1. CF adjusts the formula for each cell, just like copying and pasting a formula works on the sheet. So if you select A1:A5, and enter a DV rule equal to:

=countif($a1:$a5,a1)=1

then in A1 it's:
=countif($a1:$a5,a1)=1
then in A2 it's:
=countif($a2:$a6,a2)=1
then in A3 it's:
=countif($a3:$a7,a3)=1
etc.

So you need to enter a different formula in each cell, or better, change the formula to:

=countif($a$1:$a$5,a1)=1

You could use a named range too.
 
Last edited:
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