Lookup a duplicate value in a table only once

[BarKv]

I have a dataset consisting of approx 200,000 rows. One of the columns is named ProjectNumber, and if I remove the duplicates there is approx 2,000 unique values left. I have a lookup formula to another table with projects, to check if the ProjectNumber exists. I know how to do the lookup formula itself (using MATCH), but the formula takes 7 seconds to finish up checking every of the 200,000 rows. In comparison, when I remove the duplicates, and check only the 2,000 remaining rows, the formula takes less than 0,1 seconds. (I'm using a RangeTimer macro to measure the time.) So, my worksheet with all the 200,000 rows is very slow :/

I know how to remove the duplicates, but I'm making this sheet for others to use, and I would like an error message to be displayed in the table with the 200,000 rows. I only need one of the rows with a non existing ProjectNumber to display the error message.

So, my question is this: Is there any formula that can do a lookup for the ProjectNumber, but if the same ProjectNumber already has been checked, then the formula should do nothing. So basically, I need a formula that checks a duplicate value only once.

What I have tried:

• IF(ROW([@ProjectNumber])-1=MATCH([@ProjectNumber],[ProjectNumber],0),"Lookup","Do not lookup")
  This formula only does a lookup if the row number equals the row where the ProjectNumber first appears. However, the MATCH part is doing what I'm trying to avoid in the first place, by checking the entire 200,000 rows, for each row. So, this formula also slows Excel down.

Any ideas?

 

[BarKv]

I should also mention that I'm trying to solve this with a worksheet formula.

 

[Aladin Akyurek]

Care to post a sample of the data and the output area if it's within the table you seem to have?

 

[Tim_Excel_]

I'm not too certain if I understand what you are trying to accomplish. Perhaps you could stop the formula from executing by starting off with a an IF functions that counts the amount of rows, and only when the amount is smaller than x (IF=False), the rest of the formula is executed

 

[BarKv]

Care to post a sample of the data and the output area if it's within the table you seem to have?

I can try. Not sure what you want here, but is this ok?

ProjectNumber	Check if ProjectNumbers exists in another table
1	Error: This number does not exist
1	Error: This number does not exist
1	Error: This number does not exist
1	Error: This number does not exist
2
2
2
3	Error: This number does not exist
4

<tbody>
</tbody>

So, for all the rows with ProjectNumber=1, I only want to check one of them, and one error message in total for ProjectNumber=1.

 

[BarKv]

I'm not too certain if I understand what you are trying to accomplish. Perhaps you could stop the formula from executing by starting off with a an IF functions that counts the amount of rows, and only when the amount is smaller than x (IF=False), the rest of the formula is executed

I tried a IF(COUNTIF(, but it looks like the COUNTIF also needs to go through every of the 200,000 rows for each row. Is there any way to do a count and stop counting if the count reaches 2 or higher?

 

[Aladin Akyurek]

I can try. Not sure what you want here, but is this ok?

ProjectNumber	Check if ProjectNumbers exists in another table
1	Error: This number does not exist
1	Error: This number does not exist
1	Error: This number does not exist
1	Error: This number does not exist
2
2
2
3	Error: This number does not exist
4

<tbody>
</tbody>

So, for all the rows with ProjectNumber=1, I only want to check one of them, and one error message in total for ProjectNumber=1.

Just post what the second column must show...

 

[BarKv]

Just post what the second column must show...

Sure

ProjectNumber	Check if ProjectNumbers exists in another table
1	Error: This number does not exist
1
1
1
2
2
2
3	Error: This number does not exist
4

<tbody>
</tbody>

 

[Tim_Excel_]

=LOOKUP(2,1/(A:A<>""),ROW(A:A))

Tested with 200,000 rows, took a split second

 

[Aladin Akyurek]

Sure

ProjectNumber	Check if ProjectNumbers exists in another table
1	Error: This number does not exist
1
1
1
2
2
2
3	Error: This number does not exist
4

<tbody>
</tbody>

In B2 enter and copy down:

=IF(ISNA(MATCH(A2,$A$1:A1,0)),IF(ISNA(VLOOKUP(A2,Table,1,0)),"Error: This number does not exist",""),"")