Right structure for a series of dates: values - json

Question

I'm having a hard time trying to figure out what is the right JSON structure for the following set of data. I've got a sensor that logs humidity of a given room on a daily basis. Logs look like:
...
2015-01-19 8%
2015-01-20 13%
...
I'd like to convert it to JSON. My first bet was:
{
'2015-01-19': 8,
'2015-01-20': 13
}
But, is it correct? Shouldn't it be:
[
{ '2015-01-19', 8 },
{ '2015-01-20', 13}
]
Or:
[
{
'date': '2015-01-19',
'value': 8
},
{
'date': '2015-01-20',
'value': 13
}
]
And, at the end of the day, is there a series of best practices I could refer to in order to help me determine what's the best structure on my own?

Answer 1

Your first example is simple and easy, though perhaps not extensible if you decide to add more attributes later. If that's unlikely, you should use that method.
Your second example is not valid JSON.
Your third example makes some sense, though it is not a very compact encoding (wastes space).
A fourth method you should consider is to use separate arrays. This is not necessarily intuitive at first, but it does work well, is compact yet extensible, and is directly compatible with some tools such as HighCharts. That is:
{
'dates': ['2015-01-19', '2015-01-20'],
'humidity': [8, 13]
}