Data Types and Roles in Tableau
In Tableau, there are several data types that are supported. For example, you may have text values, date values, numerical values, and more. Each of the data types can take on different roles that dictate their behavior in the view.
All fields in a data source have a data type. The data type reflects the kind of information stored in that field, for example integers (410), dates (1/23/2005) and strings (“Wisconsin”).
Mixed Data Types for Excel and CSV Files
Most columns in an Excel or CSV (comma separated value) file contain values of the same data type (dates, numbers, text). When you connect to the file, Tableau creates a field in the appropriate area of the Data window for each column. Dates and text values are dimensions, and numbers are measures.
However, a column might have a mixture of data types such as numbers and text, or numbers and dates. When you connect to the file, the mixed-value column is mapped to a field with a single data type in Tableau. Therefore, a column that contains numbers and dates might be mapped as a measure or it might be mapped as a date dimension. The mapping is determined by the data types of the first 16 rows in the data source.
Example: if most of the first 16 rows are text values, then the entire column is mapped as text.
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Empty cells also create mixed-value columns because their formatting is different from text, dates, or numbers.
Depending on the data type Tableau determines for each field, the field might contain Null values for the other (non matching) records as described in the table below.
|Text||Text is treated as Null. A number is treated as the day in numeric order from 1/1/1900. You can identify these values by creating a row or column header with the field.|
|Dates||and numbers are treated at text. Nulls are not created.|
If using fields that are based on mixed-value columns introduces difficulties when analyzing your data, you can:
• Format empty cells in your underlying data source so they match the data type of the column.
• Create a new column in Excel that does not contain mixed values.
In addition to a data type, every field in Tableau is characterized by two important additional settings that determine the role and behavior of the field when it is placed on a shelf.
To expose the full functionality of Tableau it is useful to control whether a field is a dimension or measure, and continuous or discrete.
On a multidimensional data source, changing data roles is limited. You can change some measures from continuous to discrete, but in general data roles on this type of data source cannot be changed.
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