Support of new reshaping alteration "melt"

[Seddryck]

This alteration is useful to reshape a result-set into a format where one or more columns are identifier variables, while all other columns, considered measured variables, are “unpivoted” to the row axis, leaving just two non-identifier columns, ‘variable’ and ‘value’.

Attributes:

• variable-identifier: Name to use for the ‘variable’ column. If not specified use ‘variable’.
• value-identifier: Name to use for the ‘value’ column. If not specified use ‘value’.

Elements:

• keys: Column(s) to use as identifier variables.
• values: Column(s) to unpivot. If not specified, uses all columns that are not set as keys.

Original table

Fruit	Price	Stock
Apple	10	125
Peer	22	145
Orange	5	15

Alteration

<melt variable-identifier="[attrib.]">
   <keys>
      <column identifier="#0">
   </keys>
<melt />

Result table

Fruit	attrib.	value
Apple	Price	10
Apple	Qty	125
Peer	Price	22
Peer	Qty	145
Orange	Price	5
Orange	Qty	15