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When you create or edit a transform, the data grid displays a preview of results of the transform. Transform previews assist in specifying and validating the transformation steps before they are applied. Although final results may not be exactly represented, a preview gives a good indication of the changes. 

When you review a preview column, keep the following in mind: 

  • You cannot rename or change the data type of a previewed column until you add the change to your recipe.
  • Selection of column headers is disabled.

For example, you want to remove leading and trailing quotation marks from all columns. You highlight the quotation marks in one cell and select a transform card for Replace:

Figure: Replace Transform Card

 

The transform preview displays in the data grid for each column to be modified:

Tip: The preview also contains updated data quality bars and column histograms. So, you can cut and then paste the step again to see changes in these visual counts in the preview.

 

Figure: Transform Preview for Replace

The transform preview displays for all valid transforms.

Tip: Press ESC to cancel a preview.

 

When you edit a transform, the Transform Editor validates the transform as you type. 

  • You can review the preview results using independent scroll bars in the transform preview.
    • Previews of single column transforms are displayed next to the source column.
    • Previews of multi-column transforms are displayed at the end of the dataset.
  • Any filters applied through the filter box apply to the transform preview only.

Preview color scheme:

ColorMeaning
bluematching data
yellowupdated data
greenunchanged data
reddeletions
blurredtransform is invalid

An error might appear while you are typing the transform. Because the transform is not valid, the transform preview appears blurred and does not display the results of the transform.

Variations:

Previews vary depending on the type of transform. For example, if you create a transform to replace values in a column, the preview displays the results of that transform. If you create a transform to extract values from a column, the preview displays the values that will be extracted.

 

Split pane previews: For transforms that change the number of rows and columns, the results of the transform are previewed in a split pane view in the Data Grid and in the Column Browser. The following transform types are previewed in a split pane: 
  • aggregate
  • deduplicate
  • unpivot

Figure: Split Pane Preview

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