19 Sep 2017

Neo4j: Cypher - Create Cypher map with dynamic keys

I was recently trying to create a map in a Cypher query but wanted to have dynamic keys in that map. I started off with this query:

WITH "a" as dynamicKey, "b" as dynamicValue
RETURN { dynamicKey: dynamicValue } AS map


╒══════════════════╕
│"map"             │
╞══════════════════╡
│{"dynamicKey":"b"}│
└──────────────────┘

Not quite what we want! We want dynamicKey to be evaluated rather than treated as a literal. As usual, APOC comes to the rescue!

In fact APOC has several functions that will help us out here. Let’s take a look at them:

CALL dbms.functions() yield name, description
WHERE name STARTS WITH "apoc.map.from"
RETURN name, description

╒═════════════════════╤═════════════════════════════════════════════════════╕
│"name"               │"description"                                        │
╞═════════════════════╪═════════════════════════════════════════════════════╡
│"apoc.map.fromLists" │"apoc.map.fromLists([keys],[values])"                │
├─────────────────────┼─────────────────────────────────────────────────────┤
│"apoc.map.fromNodes" │"apoc.map.fromNodes(label, property)"                │
├─────────────────────┼─────────────────────────────────────────────────────┤
│"apoc.map.fromPairs" │"apoc.map.fromPairs([[key,value],[key2,value2],...])"│
├─────────────────────┼─────────────────────────────────────────────────────┤
│"apoc.map.fromValues"│"apoc.map.fromValues([key1,value1,key2,value2,...])" │
└─────────────────────┴─────────────────────────────────────────────────────┘

So we can generate a map like this:

WITH "a" as dynamicKey, "b" as dynamicValue
RETURN apoc.map.fromValues([dynamicKey, dynamicValue]) AS map

╒═════════╕
│"map"    │
╞═════════╡
│{"a":"b"}│
└─────────┘

or like this:

WITH "a" as dynamicKey, "b" as dynamicValue
RETURN apoc.map.fromLists([dynamicKey], [dynamicValue]) AS map

╒═════════╕
│"map"    │
╞═════════╡
│{"a":"b"}│
└─────────┘

or even like this:

WITH "a" as dynamicKey, "b" as dynamicValue
RETURN apoc.map.fromPairs([[dynamicKey, dynamicValue]]) AS map

╒═════════╕
│"map"    │
╞═════════╡
│{"a":"b"}│
└─────────┘

About the author

I'm currently working on short form content at ClickHouse. I publish short 5 minute videos showing how to solve data problems on YouTube @LearnDataWithMark. I previously worked on graph analytics at Neo4j, where I also co-authored the O'Reilly Graph Algorithms Book with Amy Hodler.