Develop Reference

Getting the key with largest value from aggregate_histogram result in Google Earth Engine

In Google Earth Engine, I am getting an object obj from an aggregate_histogram call, and print(obj) shows the following:
{
"115.0": 1,
"137.0": 1,
"35.0": 137,
"42.0": 164
}
I would like to extract the key for which the value is largest, so "42.0" (which should please most everyone as the correct answer to any big question).
How can I proceed?
I know how to do it in pure JavaScript, but here it doesn't look like it works:
print(Object.keys(obj)) // yields "[]"
EDIT: adding more info after the first answer by Kosh.
var obj = loc.aggregate_histogram('relativeOrbitNumber_start')
var o = {
"115.0": 1,
"137.0": 1,
"35.0": 137,
"42.0": 164
};
print(o)
print(obj)
print(Object.keys(o))
print(Object.keys(obj))
This yields the following:
screenshot

It seems that it has to do with client- and server-side variables.
So service-side processing steps are required.
Here is something that seems to work:
var o = ee.Dictionary(loc.aggregate_histogram('relativeOrbitNumber_start'))
var okeys = ee.List(o.keys())
var ovals = ee.List(o.values())
var minmax = ee.Dictionary(ovals.reduce(ee.Reducer.minMax()))
var maxval = ee.Number(minmax.get('max'))
var maxind = ovals.indexOf(maxval)
var maxkey = okeys.get(maxind)
print('maxkey:', maxkey)
Unfortunately, this variable then can't be used as input to filterMetadata:
// this yields an empty collection, where maxKey = 42.0:
var sel = loc.filterMetadata('relativeOrbitNumber_start', 'equals', maxKey)
// this yields a non-empty collection:
var sel = loc.filterMetadata('relativeOrbitNumber_start', 'equals', 42.0)
So I first have to get it into the client side by using getInfo, as per this answer.
var ms = maxKey.getInfo() // local string
var mi = parseInt(ms) // local integer
// this yields a non-empty collection:
var sel = loc.filterMetadata('relativeOrbitNumber_start', 'equals', mi)
This seems like a bug though, why wouldn't filterMetadata be able to accept server-side variables as arguments? Especially since using getInfo() is discouraged in the documentation. 🤷

Using reduce:
const o = {
"115.0": 1,
"137.0": 1,
"35.0": 137,
"42.0": 164
};
const max = Object.keys(o).reduce((m, k) => o[m] > o[k] ? m : k)
console.log(max)

Weird comparison performance on Javascript object key lookup

Presentation :
I am working on a piece of code that can compare two javascript Object by looping into the first one (called A) to perform a key lookup in the second one called B (I put value as key and occurence as value).
But when I am measuring the performance of the subkey key lookup of Object A (10 times per amount of data, with data as changing parameters for each 10 times the program runs (100 per row, 200...) I get high timing for the smallest amount of data (so potentially less key in the dict B)
Objects layout :
Object A looks like below:
{
SQL_TABLE_1:
{
column_1:
[
'2jmj7l5rSfeb/vlWAYkK/YBwIDk=',
'3MaRDFGBKvsLLhrLUdplz3wUiOI=',
'PEvUFHDR4HbOYXcj7danOvyRJqs='
'XHvERAKZ4AqU+iWlx2scZXdem80=',
'nSG0lvwlkIe5YxZGTo5binr3pAw=',
'Swuc/7YCU9Ptfrff+KHaJJ1+b7U=',
'N28qqdfezfZbPmK7CaGmj7m7IOQ=',
'ffc7skeffegT1ZytAqjco3EpwUE=',
'2XldayBefzBxsUuu6tMFYHVZEEY=',
'5rC2y6IzadQ1aEy7CvNyr30JJ2k='
]
},
SQL_TABLE_2:
{
column_1:[......]
}
}
Object B field have various size but this size never change in our tests
And Object B looks like:
[
field_1:
{
'2jmj7l5rSfeb/vlWAYkK/YBwIDk=': 1,
'3MaRDFGBKvsLLhrLUdplz3wUiOI=': 1,
'PEvUFHDR4HbOYXcj7danOvyRJqs=': 1,
'XHvERAKZ4AqU+iWlx2scZXdem80=': 4,
'nSG0lvwlkIe5YxZGTo5binr3pAw=': 1,
'Swuc/7YCU9Ptfrff+KHaJJ1+b7U=': 1,
'N28qqdfezfZbPmK7CaGmj7m7IOQ=': 27,
'ffc7skeffegT1ZytAqjco3EpwUE=': 1,
'2XldayBefzBxsUuu6tMFYHVZEEY=': 18,
'5rC2y6IzadQ1aEy7CvNyr30JJ2k=': 1 },
field_2:{......}
]
Timing measurement in the code is structured like this:
sql_field_1:
{
mongo_field_1: 0.003269665241241455, mongo_field_2: 0.0015446391105651855, mongo_field_3: 0.0009834918975830079, mongo_field_4: 0.0004488091468811035,
},
sql_field_2:
{
....
}
Goal
The goal is to perform for each sub-subkey of Object A a key lookup on the Object B subkeys.
Code
Here's the code that cause this behavior:
Object A is called sql_dict_array
Object B is called hash_mongo_dict
for(var field_name in hash_mongo_dict)
{
performance_by_mongo_field[field_name] = {};
result_by_mongo_field[field_name] = {};
// LOOP ON OBJECT A KEYS
for(var table_name in sql_dict_array)
{
// Start of time measurement
var start_time = performance.now();
// there is only one column in our test data
for(var column_name in sql_dict_array[table_name])
{
found_count = 0;
for(var value of sql_dict_array[table_name][column_name])
{
// **SUBKEY LOOPKUP HERE WITH VALUE**
var results = hash_mongo_dict[field_name][value];
// IF NOT UNDEFINED THEN IT HAS BEEN FOUND
// THIS CHECK IS NOT THE BOTTLENECK
if(results != undefined)
{
found_count+=results;
}
}
if(found_count > limit_parameter)
{
console.log("error: too many match between hashes")
process.exit(0)
}
// PERFORMANCE CALCULATION
performance_by_mongo_field[field_name][table_name] = (performance.now() - start_time)/1000;
result_by_mongo_field[field_name][table_name+'.'+column_name] = (found_count/verif_hash_count*100);
}
}
return some results...
}
Testing:
With this code, I expect to have almost constant time whatever the size of the Object B (amount of subkey) but in my code I have higher time when I have only 10 subkeys in the nested object A, and it become stable when reaching 100 keys or more (tested with 6000 keys)
Here's 10 runs for the key lookup code of one key of Object A containing 10 subkeys with 300.000+ data from Object B:
0.2824700818061829 0.2532380700111389 0.2455208191871643 0.2610406551361084 0.2840422649383545 0.2344329071044922 0.2375670108795166 0.23545906591415405 0.23111085414886476 0.2363566837310791
Here's the same comparison but with 4000+ subkeys:
0.0027927708625793456 0.0018292622566223144 0.015235211849212647 0.0036304402351379395 0.002919149875640869 0.004972007751464844 0.014655702114105225 0.003572652339935303 0.0032280778884887697 0.003232938766479492
I will appreciate every advice you can provide me,

How to convert arrays to objects in javascript?

How could I rewrite this code to object javascript. Since Array usage is prohibed, I can only use objects here. Insted of pushing values to array, I would like to push this values into objects.
var container = [];
document.addEventListener("submit", function(e){
e.preventDefault();
});
window.addEventListener("load",function(){
var submit = document.getElementsByClassName("btn-primary");
submit[0].addEventListener("click",add,false);
document.getElementById("pobrisi").addEventListener("click",deleteAll,false);
var dateElement = document.getElementById('datum');
dateElement.valueAsDate = new Date();
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1;
var yyyy = today.getFullYear();
if(dd<10){
dd='0'+dd
}
if(mm<10){
mm='0'+mm
}
today = yyyy+'-'+mm+'-'+dd;
dateElement.setAttribute("min",today);
});
function add() {
var title = document.getElementById("title").value;
var type = document.getElementById("type").value;
var datum = document.getElementById("datum").value.split("-");
datum = datum[2]+". "+datum[1]+". "+datum[0];
var data = new Book(title,type,datum);
container.push(data.add());
display();
}
function display(data) {
var destination = document.getElementById("list");
var html = "";
for(var i =0;i <container.length; i++) {
html +="<li>"+container[i]+"</li>";
}
destination.innerHTML = html;
}
function deleteAll(){
container=[];
document.getElementById("list").innerHTML="";
}
Wondering if is possible to write this code whitout any array usage.

initial remarks
The problem here, in my estimation, is that you haven't learned the fundamentals of data abstraction yet. If you don't know how to implement an array, you probably shouldn't be depending on one quite yet. Objects and Arrays are so widespread because they're so commonly useful. However, if you don't know what a specific data type is affording you (ie, what convenience does it provide?), then it's probable you will be misusing the type
If you take the code here but techniques like this weren't covered in your class, it will be obvious that you received help from an outside source. Assuming the teacher has a curriculum organized in a sane fashion, you should be able to solve problems based on the material you've already covered.
Based on your code, it's evident you really have tried much, but why do you think that people here will come up with an answer that your teacher will accept? How are we supposed to know what you can use?
a fun exercise nonetheless
OK, so (we think) we need an Array, but let's pretend Arrays don't exist. If we could get this code working below, we might not exactly have an Array, but we'd have something that works like an array.
Most importantly, if we could get this code working below, we'd know what it takes to make a data type that can hold a dynamic number of values. Only then can we begin to truly appreciate what Array is doing for us.
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
// should output
// 1
// 2
// 3
runnable demo
All we have to do is make that bit of code (above) work without using any arrays. I'll restrict myself even further and only use functions, if/else, and equality test ===. I see these things in your code, so I'm assuming it's OK for me to use them too.
But am I supposed to believe your teacher would let you write code like this? It works, of course, but I don't think it brings you any closer to your answer
var empty = function () {}
function isEmpty (x) {
return x === empty
}
function pair (x,y) {
return function (p) {
return p(x,y)
}
}
function head (p) {
return p(function (x,y) {
return x
})
}
function tail (p) {
return p(function (x,y) {
return y
})
}
function push (l, x) {
if (isEmpty(l))
return list(x)
else
return pair(head(l), push(tail(l), x))
}
function list (x) {
return pair(x, empty)
}
function listeach (l, f) {
if (isEmpty(l))
return null
else
(f(head(l)), listeach(tail(l), f))
}
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
closing remarks
It appears as tho you can use an Object in lieu of an Array. The accepted answer (at this time) shows a very narrow understanding of how an object could be used to solve your problem. After this contrived demonstration, are you confident that you are using Objects properly and effectively?
Do you know how to implement an object? Could you fulfill this contract (below)? What I mean by that, is could you write the functions object, set, and get such that the following expressions evaluated to their expected result?
In case it's not obvious, you're not allowed to use Object to make it happen. The whole point of the exercise is to make a new data type that you don't already have access to
m = object() // m
set(m, key, x) // m
get(m, key) // x
set(m, key2, y) // m
get(m, key2) // y
set(m, key3, set(object(), key4, z)) // m
get(get(m, key3), key4) // z
I'll leave this as an exercise for you and I strongly encourage you to do it. I think you will learn a lot in the process and develop a deep understanding and appreciation for what higher-level data types like Array or Object give to you

Since this is a homework I feel like I shouldn't solve it for you, but rather help you in the right direction.
Like Slasher mentioned you can use objects
With JavaScript object one book would look something like
const book = {
title: 'my awesome title',
type: 'novel'
};
book is the object
title is a property with a value 'my awesome title'
type is a property with a value 'novel'
But objects can also have other objects as values. Something like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
}
};
You can reference the books in the bookshelf in two ways
const book1 = BookShelf.Book1 // Returns the book1 object
const title1 = Book1.Title; // Get the title
const sametitle = BookShelf.Book1.Title // Returns title for book1, same as above.
You can also use brackets:
const book1 = BookShelf['Book1'];
const title1 = BookShelf['Book1']['Title];
You can even make new properties on a object like this:
const Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
BookShelf['Book3'] = Book3;
Now the BookShelf has a Book3 property. So your BookShelf object looks like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
},
Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
};
That should get you started :)

JavaScript Objects is a good way to go
1- define a new object:
var myVar = {};
or
var myVar = new Object();
2- usage
// insert a new value, it doesn't matter if the value is a string or int or even another object
// set a new value
myVar.myFirstValue="this is my first value";
// get existing value and do what ever you want with it
var value = myVar.myFirstValue

Accessing a javascript object in D3.js

A javascript data object (JSON notation) has been created with the following content:
"[
{"range":"Shape","values":[{"idx":0,"val":"Random"},{"idx":1,"val":"Line"},{"idx":2,"val":"Square"},{"idx":3,"val":"Circle"},{"idx":4,"val":"Oval"},{"idx":5,"val":"Egg"}]},
{"range":"Color","values":[{"idx":0,"val":"Red"},{"idx":1,"val":"Blue"},{"idx":2,"val":"Yellow"},{"idx":3,"val":"Green"},{"idx":4,"val":"Cyan"}]}
]"
In a next step the index of an ordinal value has to be found in this object. The function should find the index of the value 'Blue' in the range 'Color'.
So the function should have the meta scripting form
f("Color")("Blue")=1
What is the most elegant form to create such a function in the context of D3 and javascript?

Depending on your use case, it might make sense to convert the data structure to a different structure more suitable for direct access. E.g. you could convert your structure to
var data = {
Shape: ['Random', 'Line', ...],
// ...
};
and access it with
data['Shape'].indexOf('Line') // or data.Shape.indexOf('Line')
Or go even one step further and convert to
var data = {
Shape: {
Random: 0,
Line: 1,
// ...
},
// ...
};
and access it with
data['Shape']['Line'] // or data.Shape.Line
What the best solution is depends on the actual use case.
Converting the structure dynamically is pretty straight forward. Here is an example to convert it to the first suggestion:
var newData = {};
data.forEach(function(item) {
newData[item.range] =
item.values.map(function(value) { return value.val; });
});
This would also reduce redundancy (e.g. idx seems to correspond with the element index).

Would this work for you ?
var dataJson = '[ \
{"range":"Shape","values":[{"idx":0,"val":"Random"},{"idx":1,"val":"Line"},{"idx":2,"val":"Square"},{"idx":3,"val":"Circle"},{"idx":4,"val":"Oval"},{"idx":5,"val":"Egg"}]},\
{"range":"Color","values":[{"idx":0,"val":"Red"},{"idx":1,"val":"Blue"},{"idx":2,"val":"Yellow"},{"idx":3,"val":"Green"},{"idx":4,"val":"Cyan"}]}\
]';
var data = JSON.parse(dataJson);
for (each in data){
if ( (data[each].range) === 'Color'){
for (eachVal in data[each].values){
if (data[each].values[eachVal].val === 'Blue'){
alert(data[each].values[eachVal].idx);
}
}
} ;
}
And here is the JSFiddle for you too.

Dictionary equivalent data structure?

I'm working in JavaScript and want to keep a list of set km/mph approximations to hand. (I can't convert programmatically, I'm working with an external API that expects certain values, so it really does have to be a dictionary equivalent.)
Currently I'm using an object:
var KM_MPH = { 10: 16, 12: 20, 15: 24 };
Going from mph to km is pretty easy:
var km = KM_MPH[10];
How do I find mph, given km? Also, is an object the best data structure to use for this sort of thing in JavaScript? I'm more used to Python.

A basic JavaScript object is in fact the best choice here. To find a reverse mapping, you can do:
function mphToKM(val){
for(var km in KM_MPH){
if(KM_MPH[km] === val){
return km;
}
}
return null;
}
Or, if you anticipate having to do a lot of lookups, I would recommend having a secondary JS Object that is the mirror of the first
var mph_km = {};
for(var km in KM_MPH){
mph_km[KM_MPH[km]] = km;
}
// mph_km[16] ==> 10
I don't know if you are in fact doing this for conversion between kilometres per hour to miles per hour... if so, it seems to make more sense to just do the conversion directly instead of relying on a hash mapping of the values.
var conversionRate = 1.609344; // kilometres per mile
function kphToMPH(val){
return val / conversionRate ;
}
function mphToKPH(val){
return val * conversionRate;
}

You can use iterate over all entries to find to find your key
Mostly a dict is used to from key=>value
Alternatively you can have two lists
var km = [];
var mph = [];
with their corresponding indices mapped

This is much closer to a Dictionary data structure, since you can have dozens of elements:
var dictionary = [
{ key: 10, value: 12 },
{ key: 12, value: 20 },
{ key: 15, value: 24 }
];
Then you can also use some JavaScript Framework like jQuery to filter elements:
var element = $.filter(dictionary, function() {
return $(this).attr("key") == 10;
});
alert($(element).attr("value"));

Yes, the JavaScript object is the correct choice.
Create a second object to do the reverse lookup:
var i, MPH_KM = {};
for(i in KM_MPH) MPH_KM[KM_MPH[i]] = i;
var mph = MPH_KM[16];

The dictionary equivalent structure for a javascript object would look like this:
var dictionary = { keys:[], values:[] };
Above structure is an equivalent of
Dictionary(Of Type, Type) **For VB.Net**
Dictionary<Type, Type>) **For C#.Net**
Hope this helps!