Repository: tinkerpop Updated Branches: refs/heads/TINKERPOP-1489 bf43cdc57 -> f2f9729cd (forced update)
Expanded more on Map merging in the collections recipe CTR Project: http://git-wip-us.apache.org/repos/asf/tinkerpop/repo Commit: http://git-wip-us.apache.org/repos/asf/tinkerpop/commit/7b37a256 Tree: http://git-wip-us.apache.org/repos/asf/tinkerpop/tree/7b37a256 Diff: http://git-wip-us.apache.org/repos/asf/tinkerpop/diff/7b37a256 Branch: refs/heads/TINKERPOP-1489 Commit: 7b37a256a1c41fb3978a0fbd5716f64a1dd5bc90 Parents: 4eb80bd Author: Stephen Mallette <sp...@genoprime.com> Authored: Wed Jan 17 16:40:09 2018 -0500 Committer: Stephen Mallette <sp...@genoprime.com> Committed: Wed Jan 17 16:40:09 2018 -0500 ---------------------------------------------------------------------- docs/src/recipes/collections.asciidoc | 47 +++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/tinkerpop/blob/7b37a256/docs/src/recipes/collections.asciidoc ---------------------------------------------------------------------- diff --git a/docs/src/recipes/collections.asciidoc b/docs/src/recipes/collections.asciidoc index 5db1e6b..61fee99 100644 --- a/docs/src/recipes/collections.asciidoc +++ b/docs/src/recipes/collections.asciidoc @@ -282,7 +282,7 @@ g.V().has('name','marko'). by(select(values).unfold()) ---- -The code above, basically deconstruct then reconstructs the `Map`. The key to the pattern is to first `unfold()` the +The code above, basically deconstructs then reconstructs the `Map`. The key to the pattern is to first `unfold()` the `Map` into its key and value entries. Then for each key and value produce a new `Map` using `group()` where the key for that map is the key of the entry (those are obviously unique as you picked them out of the `valueMap()`) and the value is simply the `unfold()` of the list of values in each entry. Recall that the `select(values).unfold()` only @@ -340,4 +340,49 @@ g.V(). group(). by(keys). by(select(values).unfold())) +---- + +As there may be a desire to remove entries from a `Map`, there may also be the need to add keys to a `Map`. The pattern +here involves the use of a `union()` that returns the `Map` instances which can be flattened to entries and then +reconstructed as a new `Map` that has been merged together: + +[gremlin-groovy,modern] +---- +g.V(). + has('name','marko'). + union(project('degree'). <1> + by(bothE().count()), + valueMap(true)). + unfold(). <2> + group(). + by(keys). + by(select(values).unfold()) +---- + +<1> The `valueMap(true)` of a `Vertex` can be extended with the "degree" of the `Vertex` by performing a `union()` of +the two traversals that produce that output (both produce `Map` objects). +<2> The `unfold()` step is used to decompose the `Map` objects into key/value entries that are then constructed back +into a single new `Map` given the patterns shown earlier. The `Map` objects of both traversals in the `union()` are +essentially merged together. + +When using this pattern, it is important to recognize that if there are non-unique keys produced by the traversals +supplied to `union()`, they will overwrite one another given the final `by()` modulator above. If changed to +`by(select(values).unfold().fold())` they will merge to produce a `List` of values. Of course, that change will bring +a `List` back for all the values of the new `Map`. With some added logic the `Map` values can be flattened out of +`List` instances when necessary: + +[gremlin-groovy,modern] +---- +g.V(). + has('name','marko'). + union(valueMap(true), + project('age'). + by(constant(100))). + unfold(). + group(). + by(keys). + by(select(values). + unfold(). + fold(). + choose(count(local).is(eq(1)), unfold())) ---- \ No newline at end of file
