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Neo4j: LOAD CSV - Column is Null

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Neo4j: LOAD CSV - Column is Null

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One problem I’ve seen a few people have recently when using Neo4j’s LOAD CSV function is dealing with CSV files that have dodgy hidden characters at the beginning of the header line.

For example, consider an import of this CSV file:

$ cat ~/Downloads/dodgy.csv
userId,movieId
1,2

We might start by checking which columns it has:

$ load csv with headers from "file:/Users/markneedham/Downloads/dodgy.csv" as line return line;
+----------------------------------+
| line                             |
+----------------------------------+
| {userId -> "1", movieId -> "2"} |
+----------------------------------+
1 row

Looks good so far but what about if we try to return just ‘userId’?

$ load csv with headers from "file:/Users/markneedham/Downloads/dodgy.csv" as line return line.userId;
+-------------+
| line.userId |
+-------------+
| <null>      |
+-------------+
1 row

Hmmm it’s null…what about ‘movieId’?

$ load csv with headers from "file:/Users/markneedham/Downloads/dodgy.csv" as line return line.movieId;
+--------------+
| line.movieId |
+--------------+
| "2"          |
+--------------+
1 row

That works fine so immediately we can suspect there are hidden characters at the beginning of the first line of the file.

The easiest way to check if this is the case is open the file using a Hex Editor – I quite like Hex Fiend for the Mac.

If we look at dodgy.csv we’ll see the following:

2014 09 24 21 20 06

Let’s delete the highlighted characters and try our cypher query again:

$ load csv with headers from "file:/Users/markneedham/Downloads/dodgy.csv" as line return line.userId;
+-------------+
| line.userId |
+-------------+
| "1"         |
+-------------+
1 row

All is well again, but something to keep in mind if you see a LOAD CSV near you behaving badly.

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Published at DZone with permission of Mark Needham, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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