xsl:for-each-group

Selects a sequence of nodes and/or atomic values and organizes them into subsets called groups.

Category: instruction
Content: ( xsl:sort* , sequence-constructor )
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element

Attributes

`select`	`expression`	Expression to select nodes/values.
`group-by?`	`expression`	Groups together all items having the same value for a grouping key. The grouping key may have multiple values (a sequence of values) in which case the item is added to more than one group.
`group-adjacent?`	`expression`	Groups together all items having the same value for a grouping key, provided that they are also adjacent in the input sequence. This is useful when you need to wrap a new element around a sequence of related elements in the source documents, for example a consecutive sequence of `<bullet>` elements. In this case the grouping key must be single-valued.
`group-starting-with?`	`pattern`	Processes the items in the supplied sequence in turn, starting a new group whenever one of the items matches a specified pattern. This is useful, for example, when matching an `<h2>` element and its following `<p>` elements.
`group-ending-with?`	`pattern`	Processes the items in the supplied sequence in turn, closing the current group whenever one of the items matches a specified pattern. This is useful when matching a sequence of items in which the last item in the group carries some distinguishing attribute such as `continued="no"`.
`composite?`	`boolean`	Can be used when grouping using either `group-by` or `group-adjacent`. If set to `yes`, then the `group-by` and `group-adjacent` expressions may evaluate to a sequence, and grouping is done by comparing the entire sequence. If set to `no` (the default), then when `group-by` evaluates to a sequence, the relevant item has multiple grouping keys and goes in multiple groups; with `group-adjacent`, a sequence-valued grouping key is then an error.
`collation?`	`{ uri }`	The name of a collating sequence, used when comparing grouping keys. Can be used when grouping using either `group-by` or `group-adjacent`. If present it must be a collation URI that uses the scheme and path `http://www.w3.org/2013/collation/UCA`, in which case it requests use of the Unicode Collation Algorithm, or is a collation otherwise recognized by Saxon: see Implementing a collating sequence.

Notes on the Saxon implementation

Earlier drafts of XSLT 3.0 introduced new attributes bind-group and bind-grouping-key; these are no longer supported since Saxon 9.6.

The composite attribute has been implemented since Saxon 9.6.

Since 9.6, Saxon supports streamed grouping when the group-adjacent, group-starting-with, or group-ending-with attributes are used, but not with a group-by attribute.

A working draft of XSLT 3.0 introduced the ability to bind variables to the current group and the current grouping key as an alternative to using the functions current-group() and current-grouping-key(), but this was later dropped from the specification. This feature was implemented in Saxon 9.6, but dropped since Saxon 9.7.

Details

There are four possible ways of defining the grouping using different attributes: group-by, group-adjacent, group-starting-with, and group-ending-with.

In XSLT 3.0, the capabilities of the xsl:for-each-group instruction are extended by virtue of the fact that the pattern used in group-starting-with or group-ending-with can now match atomic values as well as nodes.

Examples

For examples of using the instruction, see the XSLT 2.0 specification.

Links to W3C specifications

XSLT 2.0 Specification

XSLT 3.0 Specification