Mark Needham

Thoughts on Software Development

neo4j: Handling SUM’s scientific notation

without comments

In some of the recent work I’ve been doing with neo4j the queries I’ve written have been summing up the values from multiple nodes and after a certain number is reached the value returned used scientific notation.

For example in a cypher query like this:

START category = node:categories('category_id:1') 
MATCH p = category-[:has_child*1..5]->subCategory-[:has_product]->product-[:sold]->sales 
RETURN EXTRACT(n in NODES(p) : n.category_id?),subCategory.category_id, SUM(sales.sales)

I might get a result set like this:

+------------------------------------------------------------------------------------------------+
| EXTRACT(n in NODES(p) : n.category_id?)        | subCategory.category_id  | SUM(sales.sales)   |
+------------------------------------------------------------------------------------------------+
| ["246","254","255","3279",<null>,<null>]       | "3279"                   | 3.07213e07         |
| ["246","3649","3650","4362",<null>,<null>]     | "4362"                   | 1.023412e06        |
| ["246","287","291","308",<null>,<null>]        | "308"                    | 504712.5999448135  |
+------------------------------------------------------------------------------------------------+

I wanted to be able to add the first two rows together but still have them return separately which meant I needed to convert the values into decimal notation in order to do so.

I came across a Stack Overflow thread explaining how to do it in Ruby:

> "%f" % "3.07213e07"
=> "30721300.000000"

or

> "3.07213e07".to_f
=> 30721300.0

If we want to do the same thing in Java it’d read like this:

double d = Double.parseDouble("3.07213e07");
NumberFormat formatter = new DecimalFormat("###.#####");
String f = formatter.format(d);
System.out.println(f);
// returns 30721300

I couldn’t see a way to make the SUM function return in decimal notation but it’d be neat if there was a way to.

For now we have to apply some formatting on the result if we want to do any calculations with it.

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Written by Mark Needham

September 30th, 2012 at 7:47 pm

Posted in neo4j

Tagged with ,