The **Expression** column allows you to compute and derive numerical values.

Related Articles:

For more information see:

## How to create

Click the expression column button to create a new column.

Use column names from numerical columns in mathematical expressions.

Calculations are performed on each row.

## Forming expressions

The expression column uses arguments that are either columns or global variables. An expression like 2x+y, where 2x is understood as 2*x, has two arguments ‘x’ and ‘y’. If x and y are names of numerical columns, the expression column will use the rows where the x and y columns have values.

DataGraph uses standard mathematical operators, but also has a long list of built-in functions and even logical operators.

## Options

### Missing

Missing let’s the value in a column be replaced with a valid number, if it otherwise is blank.

### Type

A function can output a number or a date.

### Display

The **Display** options are different depending on the **Type**.

### # of Rows

When you enter a constant into the expression field, an additional entry box is shown that requires the number of rows to be specified.

You can enter a numerical value or global variable to return a specified number of rows.

**Example**: Set the column length equal to another column

Let’s say you want to add a constant value column with row length based on another column. You have two options:

- Set the ‘
**# of Rows**‘ to a Number from Column variable set to the length,**OR** - Use the expression ‘Data*0 + Constant’

To illustrate, see what happens when we set the expression equal to another column.

If we multiple the column values by zero, we get a column of zeros that is the same length.

We can add a constant numerical value or a column property that returns a single value.

This approach is a bit of a trick but a quick way to force the length of an expression column to come from another column.