JSONPath & XPath Expression Evaluator

About Expression Evaluator

Where the Path Finder lists matches, the evaluator reduces them to one answer. Pick a function — count, sum, avg, median, min, max, product, range, first, last, distinct, sort, join, length, keys, values, paths or types — and it is applied to everything the expression selects.

The functions work the same way in every format, because they read the matched nodes rather than the document: a JSONPath match set and an XPath node set reduce identically. Choose matches when you want the nodes themselves rather than a reduction.

XML keeps its own function library as well. An XPath that already answers — count(//item), sum(//item/@qty), string-length(//title), boolean(//error) — is reported as it stands, and the result says the function was not applied, because there was nothing left to reduce.

Where it helps

• Answers aggregate questions — how many, how much, what is the largest — without writing a script.
• Twenty functions cover counting, arithmetic, ordering, sampling and key inspection.
• The same functions apply to JSON, YAML and XML, so an XPath node set can be averaged or sorted as easily as a JSONPath match.
• XPath's native function library is still available in full for XML.
• Reports how many nodes matched alongside the answer, so an unexpected result is easy to diagnose.

Limits

• Arithmetic functions ignore matches that are not numbers rather than failing, so check the matched count against what you expected.
• The function applies to the whole match set; grouping and joins need a real query language.
• XPath here is 1.0, so its own library has no max() or min() — select the nodes and let the function list reduce them instead.
• Floating-point arithmetic applies, so summing money can produce the usual trailing-decimal artefacts.

Frequently asked questions

Why is my sum zero?

The path matched nodes that are not numbers — often objects rather than the field inside them. Check the matched count and narrow the path.

How do I count nodes in XML?

Either way works. Select them with //item and choose count, or write the XPath count(//item) and let the expression answer on its own.

What do sort and join compare?

Matches that all look numeric are ordered by size; anything else is ordered as text. join renders each match as a string and separates them with commas.

What does distinct return?

The unique values among the matches, compared structurally, so two identical objects count once.

Can I do arithmetic across two different paths?

Not here — evaluate each one and combine the answers yourself, or use a proper query tool such as jq.

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