5 Sep 2019

Neo4j: apoc.load.csv - Neo.ClientError.Statement.SyntaxError: Type mismatch: expected Float, Integer, Number or String but was Any

The Neo4j APOC library's Load CSV procedure is very useful if you want more control over the import process than the LOAD CSV clause allows. I found myself using it last week to import a CSV file of embeddings, because I wanted to know the line number of the row in the CSV file while importing the data.

I had a file that looked like this, which I put into the import directory:

$ cat import/data.csv
0.034 0.765 0.452
0.312 0.413 0.789

And before I imported it, I added the following entries to my Neo4j Settings file so that I could read locally:

apoc.import.file.enabled=true
apoc.import.file.use_neo4j_config=true

The following query processes the file, with optional config that indicates that the file doesn’t have a header and uses a space as a separator:

CALL apoc.load.csv("file:///data.csv", {header: false, sep: " "})
YIELD lineNo, map, list
RETURN lineNo, list

If we run that query we’ll get this result:

Table 1. Results
lineNo	list
0	["0.034","0.765","0.452"]
1	["0.312","0.413","0.789"]

But we want to have each item of the list be a float value rather than a string. I tried to coerce each of the values using the toFloat function:

CALL apoc.load.csv("file:///data.csv", {header: false, sep: " "})
YIELD lineNo, map, list
RETURN lineNo, [item in list | toFloat(item)] AS list

Unfortunately this doesn’t quite work, as the following error indicates:

Neo.ClientError.Statement.SyntaxError: Type mismatch: expected Float, Integer, Number or String but was Any (line 3, column 40 (offset: 129))
"RETURN lineNo, [item in list | toFloat(item)] AS list"
                                        ^

Instead we need to use APOC’s apoc.convert.toFloat function to do the type coercion. The following query does the trick:

CALL apoc.load.csv("file:///data.csv", {header: false, sep: " "})
YIELD lineNo, map, list
RETURN lineNo, [item in list | apoc.convert.toFloat(item)] AS list

Table 2. Results
lineNo	list
0	[0.034,0.765,0.452]
1	[0.312,0.413,0.789]

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.