Question: I have two columns A and B in a google spreadsheet.

I want to find all the numbers that are in column A but not in B. How do I do that?

B could have the same numbers from column A. 

So if column A has numbers: 1, 2, 3
and B has numbers 3, 4,5

I want to get all the numbers that are in A but not in B:
1, 2

How do I do that using google spread sheet?

Answer: 
Use [`MATCH`](https://support.google.com/docs/answer/3093378) to determine whether each row in column A appears in column B, then filter column A to only the rows for which [`MATCH`](https://support.google.com/docs/answer/3093378) returned `#N/A` (i.e., that row's value in column A could not be found in column B):

```
=FILTER(A:A, ISNA(MATCH(A:A, B:B, 0)))

```

If A contains duplicates and you want to reduce the result sequence to unique values, just wrap the whole thing in [`UNIQUE`](https://support.google.com/docs/answer/3093198):

```
=UNIQUE(FILTER(A:A, ISNA(MATCH(A:A, B:B, 0))))

```
In column C, use vlookup from A against B. For example

```
C1 = vlookup(A1,B:B,1)
C2 = vlookup(A2,B:B,1)
...

```

If B does not contain A, then it shows `#N/A`