# Use conditional functions in formula expressions
<a name="expression-conditional-functions"></a>

In [transforms](transforms.md) and [metrics](metrics.md), you can use the following function to check a condition and return different results, whether the condition evaluates to true or false.


| Function | Description | 
| --- | --- | 
|   `if(condition, result_if_true, result_if_false)`  |  Evaluates the `condition` and returns `result_if_true` if the condition evaluates to true or `result_if_false` if the condition evaluates to `false`. `condition` must be a number. This function considers `0` and an empty string as `false` and everything else (including `NaN`) as `true`. Booleans convert to `0` (false) and `1` (true). You can return the [none constant](expression-constants.md#none-definition) from this function to discard the output for a particular condition. This means you can filter out data points that don't meet a condition. For more information, see [Filter data points](expression-tutorials.md#filter-data). 

**Examples**  
+ `if(0, x, y)` returns the variable `y`.
+ `if(5, x, y)` returns the variable `x`.
+ `if(gt(temp, 300), x, y)` returns the variable `x` if the variable `temp` is greater than `300`.
+ `if(gt(temp, 300), temp, none)` returns the variable `temp` if it's greater than or equal to `300`, or `none` (no value) if `temp` is less than `300`. We recommend that you use UFCS for nested conditional functions where one or more arguments are conditional functions. You can use `if(condition, result_if_true)` to evaluate a condition and `elif(condition, result_if_true, result_if_false)` to evaluate additional conditions. For example, you can use `if(condition1, result1_if_true).elif(condition2, result2_if_true, result2_if_false)` instead of `if(condition1, result1_if_true, if(condition2, result2_if_true, result2_if_false))`. You can also chain additional intermediate conditional functions. For example, you can use `if(condition1, result1_if_true).elif(condition2, result2_if_true).elif(condition3, result3_if_true, result3_if_false)` instead of nesting multiple `if` statements, such as `if(condition1, result1_if_true, if(condition2, result2_if_true, if(condition3, result3_if_true result3_if_false)))`.  You must use `elif(condition, result_if_true, result_if_false)` with UFCS.   |