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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11These jq errors usually mean the filter is applying an operation to a value of the wrong type. Use .[] to iterate an array or object—not a number or string—and make both operands the same intended type before using +. Check the input shape first, then choose whether to branch on its type, normalize it, or convert values explicitly.
Why jq says it cannot iterate over a number or string
jq values have types: numbers, strings, booleans, arrays, objects, and null. The iterator .[] is for arrays and objects. If a filter applies it to a scalar such as 7 or "news", jq cannot iterate that value. See the jq development manual for jq’s value model and array construction.
This commonly happens when a field’s JSON shape is different from what the filter assumes. A field expected to contain an array may instead contain one number or string. Inspect the actual input and its type before deciding how to process it.
Choose a fix that matches the input shape
Branch when scalar and collection values need different handling
If the field may legitimately be either a scalar or an array, test its type and handle each case deliberately. For example, an array can be traversed with .[], while a scalar should be processed directly. This preserves the distinction in the input instead of silently changing its meaning.
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Normalize only when the filter should treat both cases as a collection
If downstream operations should always receive a collection, explicitly convert the scalar case into a one-element array before iterating. Apply that normalization only when treating one value as one collection item is correct for the data.
Use optional indexing for acceptable missing or non-object fields
Optional indexing, such as .foo?, can prevent an indexing operation from failing when a field is missing or its parent is not an object. It does not turn a number or string into an array, so it is not a general fix for applying .[] to a scalar. The jq 1.6 manual source documents the optional ? form.
Why adding a string and number fails
jq’s + operator depends on operand type: it adds numbers, concatenates arrays, joins strings, and merges objects. It does not automatically convert a number to text or text to a number. Consequently, adding a string and a number is a type mismatch. The jq 1.3 manual documents these type-dependent behaviors.
Decide what the result is supposed to mean before converting anything. For text output, use tostring; for arithmetic, use tonumber only when the input is known to contain valid numeric text. Converting an identifier to a number, for example, can change its meaning if leading zeroes are significant.
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Join numeric IDs as text
When a list of numeric IDs needs to become one delimiter-separated string, collect the IDs, convert each to a string, then join them:
[.topics[].id | tostring] | join(";")
The brackets collect the generated strings into an array, and join(";") combines them with semicolons. This pattern addresses the common mismatch between numeric IDs and the string values that join expects. A worked example appears in the DZone explanation of these jq errors.
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Prevent the same errors in changing JSON
- Check the field’s type and shape before using
.[]. - If both scalar and array inputs are valid, choose explicitly between branching and normalizing; do not assume they mean the same thing.
- Use optional indexing only for cases where a missing or non-object field is acceptable.
- Before using
+, make sure both operands have the intended compatible type. - Convert numeric IDs with
tostringwhen producing text; convert text withtonumberonly when it is meant to be numeric and contains valid numeric text.
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