[Decode]

var a = [{
	"Fio": "Ivanov",
	"Date": "January 16",
	"Parametr": "200"
}, {
	"Fio": "Petrov",
	"Date": "January 16",
	"Parametr": "300"
}, {
	"Fio": "Ivanov",
	"Date": "February 16",
	"Parametr": "100"
}, {
	"Fio": "Petrov",
	"Date": "February 16",
	"Parametr": "150"
}, {
	"Fio": "Ivanov",
	"Date": "March 16",
	"Parametr": "400"
}, {
	"Fio": "Petrov",
	"Date": "March 16",
	"Parametr": "500"
}, {
	"Fio": "Sidorov",
	"Date": "March 16",
	"Parametr": "300"
}];

var months = {};

a.forEach(function(item) {
	months[ item['Date'] ] = true;
});

var b = [];

Object.keys(months).forEach(function(month) {
	var newObj = {};
	newObj['Month'] = month.replace(/[\d+\s]/g, '');

	a.forEach(function(obj) {
		if (obj['Date'] == month) {
			newObj[ obj['Fio'] ] = obj['Parametr'];
		}
	});

	b.push(newObj);
});

console.log( JSON.stringify(b) );