There are multiple ways to create a calculated field in Tableau:

• Select Analysis | Create Calculated Field... from the menu.
• Use the drop-down menu next to Dimensions in the data pane:

• Right-click an empty area in the data pane and select Create Calculated Field....

• Use the drop-down menu on a field, set, or parameter in the data pane and select Create | Calculated Field....

• Double-click an empty area on the Rows, Columns, or Measure Values shelves, or in the empty area on the Marks card to create an ad hoc calculation.

When you start your calculation from an existing field or parameter, the calculation starts as a reference to that field. The calculated field you create will be part of the data source that is currently selected at the time you create it. You can edit an existing calculated field in the data pane by using the drop-down menu and selecting Edit....

The interface for creating and editing calculations looks like this:

This window has several key features:

• Calculated field name: Enter the name of the calculated field here. Once created, the calculated field will show up as a field in the data pane with the name you entered in this text box.
• Code editor: Enter code in this text area to perform the calculation. The editor includes autocomplete for recognized fields and functions. Additionally, you may drag fields, sets, and parameters from the data pane or view into the code editor to insert them into your code.

• An indicator at the bottom of the editor will alert you with errors in your code. Additionally, if the calculation is used in views or other calculated fields, you will see a drop-down indicator that will let you see the dependencies. Click the Apply button to apply changes to the calculation throughout the workbook while leaving the calculation editor open. The OK button will save the code changes and close the editor. If you wish to discard any changes you've made, click the X button in the upper-right corner to cancel changes.
• The functions list contains all of the functions that you can use in your code. Many of these functions will be used in examples or discussed in this chapter. Tableau groups various functions according to their overall use:
  • Number: Mathematical functions, such as rounding, absolute value, trig functions, square roots, and exponents.
  • String: Functions that are useful for string manipulation, such as getting a substring, finding a match within a string, replacing parts of a string, and converting a string value to uppercase or lowercase.
  • Date: Functions that are useful for working with dates, such as finding the difference between two dates, adding an interval to a date, getting the current date, and transforming strings with non-standard formats into dates.
  • Type Conversion: Functions that are useful for converting one type of field to another, such as converting integers into strings, floating point decimals into integers, or strings into dates.
  • Logical: Decision-making functions, such as if then else logic or case statements.
  • Aggregate: Functions that are used for aggregating such as summing, getting the minimum or maximum values, or calculating standard deviations or variances.
  • Pass Through: (only available when connected live to certain databases, such as SQL Server): These functions allow you to pass through raw SQL code to the underlying database and retrieve a returned value at either a row level or aggregate level.
  • User: Functions that are used to obtain usernames and check whether the current user is a member of a group. These functions are often used in combination with logical functions to customize the user's experience or to implement user-based security when publishing to Tableau Server or Tableau Online.
  • Table calculation: These functions are different from the others. They operate on the aggregated data after it is returned from the underlying data source and just prior to the rendering of the view. These are some of the most powerful functions in Tableau. We'll devote an entire chapter to them so that we can cover them.
• Selecting a function in the list or clicking a field, parameter, or function in the code will reveal details about the selection on the right. This is helpful when nesting other calculated fields in your code, when you want to see the code for that particular calculated field, or when you want to understand the syntax for a function.