Why is my array of strings encoded as a single string with "jsonencode"?

I created a struct with data:

>> data.key_a = "value_a";
>> data.key_b = ["value_b"];

Then, I encoded the struct in JSON format:

>> json = jsonencode(data);

The resulting JSON looks like this:

{"key_a":"value_a","key_b":"value_b"}

I would expect the attribute "key_b" to have a value ["value_b"] as I specified the field "key_b" to have an array of strings as its value in the "data" struct above. Why is this not the case?

Answer 1

[MathWorks Support Team]

This occurs because MATLAB doesn't make a distinction between a single (scalar) value and a 1x1 array. So, both values are encoded as JSON strings rather than JSON arrays containing a single string.

As a workaround, "key_b" could be stored as a cell array instead:

>> data.key_a = "value_a";
>> data.key_b = {"value_b"};
>> json = jsonencode(data);

This results in the desired JSON:

{"key_a":"value_a","key_b":["value_b"]}