Fold multiple columns

This processor takes values from multiple columns and transforms them to one line per column.

For example, with the following dataset representing monthly scores:

person	age	01/2014	02/2014	03/2014
John	24	3	4	3
Sidney	31		6	9
Bill	33	1		4

We would like to get one line per (month, person) couple with the score.

Applying the processor with:

• 3 columns in the “columns list”: 01/2014, 02/2014, 03/2014
• “month” as the “fold name column”
• “score” as the “fold value column”

will generate the following result:

person	age	month	score
John	24	01/2014	3
John	24	02/2014	4
John	24	03/2014	6
Sidney	31	01/2014
Sidney	31	02/2014	6
Sidney	31	03/2014	9
Bill	33	01/2014	1
Bill	33	02/2014
Bill	33	03/2014	4

• The names of the folded columns are used as values of the “fold name column”
• The values of the folded columns are used as values of the “fold values column”
• The folded columns are removed
• All other columns are copied
• Empty values are preserved in the folded result

For more details on reshaping, please see Reshaping.