Expression column

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

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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.

Number of Rows is Missing — No Data

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

Number of Rows Set to 7

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.

No Longer Requires ‘# of Rows’

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

Column of Zeros

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

Constant value with length Data

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.

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