slice: add a --json flag for JSON output

[rzmk]

Is your feature request related to a problem? Please describe.
My task requires outputting a part of a dataset as JSON and currently I use qsv slice for this, however I need to convert the sliced data to a valid JSON format which is an extra step.

Describe the solution you'd like
A --json flag for qsv slice with the output formatted like sqlp's --format json flag. No need for pretty-printing the output (could be another flag).

Describe alternatives you've considered
Potentially combining commands or if sqlp has a way to slice data based on start and end row number. Though for my purposes a --json flag would likely be the easiest to work with.

[jqnatividad]

Hi @rzmk ,

To confirm, do you want the JSON as a JSON array of arrays or as JSONL, where each JSON record is separated by newlines.

[rzmk]

An array of dictionaries where the keys of each dictionary are the headers and the values of each dictionary are that row's values.

[jqnatividad]

@rzmk, I did an implementation and it's a bit kludgy. Will keep tweaking it but have you tried piping the output of slice to qsv tojsonl?

Do you intend to use the JSON with DataTables that's why you need it in JSON array format?

[jqnatividad]

After tweaking it a bit, the implementation is much better now. The only thing it doesn't do is infer JSON types with everything as a JSON string, which for your use case, may not be required.