如何将列表（从“收集”）转换为字符串

Question

Using CYPHER I can get an ordered list of things using the collect() function. Is it possible to convert such a list into a simple string so that it behaves as a single string object?

If this isn't possible is it possible to somehow concatenate sequentially the contents of two (or more) collect statements so that in a single row I can produce output such as 'A,B,C a,b,c' where A,B,C is the ordered product of the 1st collect statement and a,b, c the second?

Answer 1

To flesh out Dave's comment: First, you'll want to combine your collections, then use REDUCE() to append each item to a string. Like so:

WITH COLLECT(first_group) AS a, COLLECT(second_group) AS b
WITH a + b AS c
WITH REDUCE(s = HEAD(c), n IN TAIL(c) | s + ', ' + n) AS result
RETURN result

Check out the docs on REDUCE to get a better idea how it works in Cypher.

Answer 2

A more general solution that will also work for collections of objects (not just collections of strings) is to convert the concatenated collections into stringified JSON using the APOC procedure apoc.convert.toJson .

This example using string collections:

WITH ['A','B','C'] AS x, ['a','b','c'] AS y, ['do','re','mi'] AS z
WITH x + y + z AS data
CALL apoc.convert.toJson(data) YIELD value
RETURN value

will return this:

"[\"A\",\"B\",\"C\",\"a\",\"b\",\"c\",\"do\",\"re\",\"mi\"]"

This example using object collections:

WITH [{a:1},{b:2},{c:3}] AS x, [{a:10},{b:20},{c:30}] AS y, [{a:100},{b:200},{c:300}] AS z
WITH x + y + z AS data
CALL apoc.convert.toJson(data) YIELD value
RETURN value

will return this:

"[{\"a\":1},{\"b\":2},{\"c\":3},{\"a\":10},{\"b\":20},{\"c\":30},{\"a\":100},{\"b\":200},{\"c\":300}]"