What You'll Learn / Key Take-Aways

- IS functions return a logical value, either TRUE or FALSE, about a specific cell or value.

- Use `ISBLANK(cell)` to detect empty cells and `ISERROR(cell)` to detect errors like #N/A, #DIV/0!, #VALUE!, etc.

- Combine checks with `OR(...)` to flag cells that are either blank or in error: `=OR(ISBLANK(G2), ISERROR(G2))`.

- Use the flagged column to filter, inspect, or remove rows with missing data.

## How IS functions work

IS functions are simple, purpose-built formulas that evaluate a single condition and return TRUE or FALSE. Syntax is straightforward: the function name, an open parenthesis, a single reference or expression, and a closing parenthesis. Examples include `ISBLANK`, `ISERROR`, `ISNUMBER`, `ISTEXT`, and `ISNA`.

Key points:

- They always return either TRUE or FALSE. These are logical values you can use directly in filters or as arguments to other functions like `OR`, `AND`, or `IF`.

- The argument you pass can be a cell reference like `G2` or an expression.

## Common IS functions you will use

- `ISBLANK(cell)`

- Returns TRUE if the cell contains no data. Note that a formula that returns an empty string is not always considered blank in every check.

- `ISERROR(cell)`

- Returns TRUE for any Excel error value such as #N/A, #VALUE!, #REF!, #DIV/0!, #NUM!, #NAME?, or #NULL!

- `ISNA(cell)`

- Returns TRUE only if the error is specifically #N/A. Use this when you only want to detect #N/A and not other error types.

- `ISNUMBER(cell)` and `ISTEXT(cell)`

- Detect the type of content in the cell.

## Practical example: Flagging missing temperature data

You have a dataset where column G contains temperature readings and column M is where you will mark missing data. The goal is to identify rows that are either blank or error values in column G.

Step-by-step:

1. In M2, start with a simple error check:

`=ISERROR(G2)`

- Returns FALSE when the value in G2 is a valid number.

- Returns TRUE when G2 contains an error like #N/A.

2. If you only want to catch blanks instead, use:

`=ISBLANK(G2)`

- Returns TRUE if G2 is empty.

3. To flag either a blank or an error, combine them with `OR`:

`=OR(ISBLANK(G2), ISERROR(G2))`

- `OR` accepts multiple logical arguments and returns TRUE if any argument is TRUE.

- You can type `G2` or click the cell when building the formula; both work the same.

4. Fill the formula down the column. Now you have a TRUE/FALSE marker for missing data.

5. Use Excel's Filter on column M to show only TRUE rows and inspect or remove those records as needed.

This approach is fast and explicit. It lets you spot which dates or rows have incomplete temperature readings so you can take action.

## When to use ISERROR vs ISNA vs IFERROR

- `ISERROR` catches all error types. Use it when any error should be treated as missing data.

- `ISNA` catches only the #N/A error. Use this when #N/A has semantic meaning and other errors should be handled differently.

- `IFERROR(value, fallback)` is an alternative that returns a fallback value instead of a logical TRUE/FALSE. Use `IFERROR` to replace errors directly, for example `=IFERROR(G2, "Missing")`.

## Additional Tips, Pitfalls to Avoid & Pro Advice

- Blank is not always the same as empty string. A cell with a formula returning `""` may not behave exactly like a truly empty cell in some checks. Test with your dataset.

- `ISBLANK` will return FALSE for cells that contain spaces. If you suspect hidden spaces, use `TRIM` or check `LEN(cell)` to detect nonzero length.

- If you only want to detect #N/A, prefer `ISNA` over `ISERROR` so you do not mask other problems.

- When cleaning data, consider combining these checks with `IF` to create readable labels instead of TRUE/FALSE. For example:

`=IF(OR(ISBLANK(G2), ISERROR(G2)), "Missing", "OK")`

- Use the flagged column to create filters or pivot segments so you never accidentally include incomplete rows in analysis.

## FAQ

Q: How do I check if a cell is blank in Excel?

A: Use `ISBLANK(cell)`. It returns TRUE if the cell has no value. Remember that a formula that returns an empty string may not be treated as blank by all functions.

Q: What is the difference between ISERROR and ISNA?

A: `ISERROR` returns TRUE for any Excel error type. `ISNA` returns TRUE only when the error is #N/A. Use `ISNA` when you specifically want to detect #N/A.

Q: How do I flag a cell that is either blank or contains an error?

A: Combine checks with `OR`, for example `=OR(ISBLANK(G2), ISERROR(G2))`. That returns TRUE if either condition is met.

Q: Can I use IS functions inside IF statements?

A: Yes. For example `=IF(OR(ISBLANK(G2), ISERROR(G2)), "Missing", "OK")` returns a text label instead of TRUE/FALSE.

Q: Why does ISBLANK return FALSE even though the cell looks empty?

A: The cell may contain a formula that returns an empty string, a space character, or invisible characters. Check with `LEN(cell)` or remove formulas to confirm.

Q: Should I use IFERROR to handle missing data?

A: `IFERROR` replaces an error with a fallback value. Use it if you want to provide an alternate value rather than a flag. Be careful as it hides all error types, which can make debugging harder.

## Summary of Key Points / Take-Home Messages

- IS functions are simple TRUE/FALSE checks that make data validation and cleaning easier.

- Use `ISBLANK` to detect empty cells and `ISERROR` to detect any errors. Use `ISNA` when you only want #N/A.

- Combine with `OR` to flag any cell that is blank or in error: `=OR(ISBLANK(G2), ISERROR(G2))`.

- Use the flagged column to filter, inspect, or remove incomplete rows before analysis.

- Consider `IFERROR` and `IF` when you want to replace or label missing values rather than just flagging them.