Variable `times` not defined

I'm trying to write code where a query is executed three times and the average execution time is displayed.

The error is:

Variable `times` not defined (line 14, column 6 (offset: 257))
"WITH times, i, end_time - start_time AS execution_time"

Can you help me please :)

Here's the code:

WITH []
AS times

UNWIND range(1,3) AS i
WITH times, i

WITH apoc.date.currentTimestamp() AS start_time

MATCH (a:Article)
WHERE a.appearsInJournal = "Journal of Science"
RETURN a.title, a.publicationDate

WITH apoc.date.currentTimestamp() AS end_time
WITH times, i, end_time - start_time AS execution_time
SET times = times + execution_time

WITH times, avg(times) AS avg_time

RETURN toFloat(avg_time)

Solution

[UPDATED]

A WITH clause will drop all existing variables, except for the ones that are specified in the WITH clause. Not all your WITH clauses are specifying times. That explains your error message.

But your main question is about how to use Cypher to determine the average execution time for a Cypher query.

Here is one approach. It executes your query 5 times and returns the average execution time in milliseconds, ignoring the timing of the first execution (with is generally more expensive due to the extra overhead to preprocess a Cypher query that has not been seen recently):

WITH '
  MATCH (a:Article)
  WHERE a.appearsInJournal = "Journal of Science"
  RETURN a.title, a.publicationDate
' AS query
UNWIND RANGE(1, 5) AS i
WITH i, query, datetime.realtime().epochMillis AS start
CALL apoc.cypher.doIt(query, NULL) YIELD value
WITH i, MAX(datetime.realtime().epochMillis-start) AS execTime
SKIP 1
RETURN AVG(execTime)

This approach also includes the time to execute the apoc.cypher.doIt procedure as well, but that overhead seems to be under a millisecond. Also, this approach only seems to work if query returns non-NULL results.