Q:

Transform JavaScript Array, create tabular view

I've searched through similar questions and tried to solve the issue on my own, but my programming skills are weak. 
I have an array like:
[{"city": "Amsterdam", "year": "2013", "amount": "450"},
 {"city": "Rotterdam", "year": "2013", "amount": "620"},
 {"city": "Geneva",    "year": "2014", "amount": "530"},
 {"city": "Rotterdam", "year": "2015", "amount": "350"}]

and I want to transform it using "city" and "year" to get "amounts". E.g. Rotterdam:[620,N/A,350]. "N/A" because value for year 2014 is missing. 
I was checking map function etc. but my skills are to weak. 
In the end I want to create a tabular view with years (horizontal) and cities (vertical).
Please advice. Thanks

A:

I don't think this is programming skills but algorithm skills. Here is a code doing what you want:

var amounts = [{"city": "Amsterdam", "year": "2013", "amount": "450"},{"city": "Rotterdam", "year": "2013", "amount": "620"},{"city": "Geneva", "year": "2014", "amount": "530"},{"city": "Rotterdam", "year": "2015", "amount": "350"}],
    formattedAmounts = {}
;
             
for (var i = 0; i < amounts.length; i++) {
    var amount = amounts[i];
  
    if (undefined === formattedAmounts[amount.city]) {
        formattedAmounts[amount.city] = {};
    }

    formattedAmounts[amount.city][amount.year] = amount.amount;
}

console.log(JSON.stringify(formattedAmounts));
alert(JSON.stringify(formattedAmounts));

function getCityAmount(city) {
    var years = [2013, 2014, 2015],
        cityAmounts = []
    ;

    for (var i = 0; i < years.length; i++) {
        cityAmounts.push(
            formattedAmounts[city] && formattedAmounts[city][years[i]]
                ?  formattedAmounts[city][years[i]]
                : 'N/A'
        );
    }

    return cityAmounts;
}

console.log(JSON.stringify(getCityAmount('Amsterdam')));
alert(JSON.stringify(getCityAmount('Amsterdam')));

function getCitiesAmounts() {
    var citiesAmounts = [];

    for (var i = 0; i < amounts.length; i++) {
        citiesAmounts.push(getCityAmount(amounts[i].city));
    }

    return citiesAmounts;
}

console.log(JSON.stringify(getCitiesAmounts()));
alert(JSON.stringify(getCitiesAmounts()));

