I have a scenario like this------
right = some_function (some_value)
var idR =right.split('~')[0];
var r =right.split('~')[1];
left = another-func (some_value)
var idL = left.split('~')[0];
var l = left.split('~')[1];
point to be noted that r,l contains numeric values.
My purpose is that I want to take the maximum between r and l, and after that I will traverse back to 'right' or 'left' according to maximum value of r or l.
I am using math.max() but this is not working as it only returns the value, not the name of variable.
How can I achieve my goal???
Let me provide some sample inputs and outputs--
"some_function" returns a string in the format "id~value" where "id" can be "1-1", "2-2" and so on and "value" can be any numeric value. I need to look at the greater "value" and fetch its corresponding "id". Note that "another_func" returns values in same pattern
MY CODE IS NOT THESE TWO BLOCKS ONLY, I HAVE EIGHT FUNCTIONS LIKE THESE AND I HAVE TO TAKE THE BIGGEST NUMBER AND ITS CORRESPONDING ID
Your question is not very clear.
Let's try this, so you have 2 arrays with values r and l and 2 arrays with variable names idR and adL.
Now this is what's not clear, do those arrays containing variable names have the same order? the same values? can this condition be trusted?
You clearly want to get some max value from the values arrays that's ok, but you aren't explaining how the other arrays fit on the picture :) After you do, probably me or someone else can help you :)
Related
I have a 2d array that I am attempting to sort.
The array is typically accessed with this structure: array[r][c].
I want to re-order the values of array, so that each [r] value is sorted by the 4th c value.
Looking online, I've seen a few sorting scripts that seem to work for other structured arrays, but I'm wondering if i'm missing something stupid.
The array is structured so that for each 'r' value in array, there is a list of values, depending on what 'c' value you put in (eg: if you do array[0][2] that will be the first entry's address, and array[0][10] is the first entry's phone number).
I want to be able to sort based off of c values 4 and... 10 (for example). (ideally, I'd sort by multiple columns, such as sort by last name first, then by first name--but i'll settle for one sort for now hahaha )
I'm not certain if any of the default sort functions would work for me, or if i need to write out a manual sort function (which i'm hoping i do not have to do as that would be fairly inefficient).
Thanks for any pointers
You'll need to write your own compare function.
Snippet:
const COLTOSORT = 2;
function compare(row1, row2) {
return row1[COLTOSORT] < row2[COLTOSORT]
? -1
: row1[COLTOSORT] > row2[COLTOSORT]
? 1
: 0;
}
array.sort(compare);
References:
Array#sort
I have a string which is name=noazet difficulty=easy and I want to produce the two words noazet and easy. How can I do this in JavaScript?
I tried var s = word.split("=");
but it doesn't give me what I want .
In this case, you can do it with that split:
var s = "name=noazet difficulty=easy";
var arr = s.split('=');
var name = arr[0]; //= "name"
var easy = arr[2]; //= "easy"
here, s.split('=') returns an array:
["name","noazet difficulty","easy"]
you can try following code:
word.split(' ').map(function(part){return part.split('=')[1];});
it will return an array of two elements, first of which is name ("noazet") and second is difficulty ("easy"):
["noazet", "easy"]
word.split("=") will give you an array of strings which are created by cutting the input along the "=" character, in your case:
results = [name,noazet,difficulty,easy]
if you want to access noazet and easy, these are indices 1 and 3, ie.
results[1] //which is "noazet"
(EDIT: if you have a space in your input, as it just appeared in your edit, then you need to split by an empty string first - " ")
Based on your data structure, I'd expect the desired data to be always available in the odd numbered indices - but first of all I'd advise using a different data representation. Where is this string word coming from, user input?
Just as an aside, a better idea than making an array out of your input might be to map it into an object. For example:
var s = "name=noazet difficulty=easy";
var obj = s.split(" ").reduce(function(c,n) {
var a = n.split("=");
c[a[0]] = a[1];
return c;
}, {});
This will give you an object that looks like this:
{
name: "noazert",
difficulty: "easy"
}
Which makes getting the right values really easy:
var difficulty = obj.difficulty; // or obj["difficulty"];
And this is more robust since you don't need to hard code array indexes or worry about what happens if you set an input string where the keys are reversed, for example:
var s = "difficulty=easy name=noazet";
Will produce an equivalent object, but would break your code if you hard coded array indexes.
You may be able to get away with splitting it twice: first on spaces, then on equals signs. This would be one way to do that:
function parsePairs(s) {
return s.split(' ').reduce(
function (dict, pair) {
var parts = pair.split('=');
dict[parts[0]] = parts.slice(1).join('=');
return dict;
},
{}
);
}
This gets you an object with keys equal to the first part of each pair (before the =), and values equal to the second part of each pair (after the =). If a string has multiple equal signs, only the first one is used to obtain the key; the rest become part of the value. For your example, it returns {"name":"noazet", "difficulty":"hard"}. From there, getting the values is easy.
The magic happens in the Array.prototype.reduce callback. We've used String.prototype.split to get each name=value pair already, so we split that on equal signs. The first string from the split becomes the key, and then we join the rest of the parts with an = sign. That way, everything after the first = gets included in the value; if we didn't do that, then an = in the value would get cut off, as would everything after it.
Depending on the browsers you need to support, you may have to polyfill Array.prototype.reduce, but polyfills for that are everywhere.
I am using the following pattern to index an injection from pairs of numbers to numbers:
var myHash = {};
...
for (... billion of iterations ...)
var x = someNum;
var y = otherNum;
myHash[x + "," + y] = z;
The problem with this code is that I'm using a string as the key of myHash, which has been tested to be much slower than integer keys. My question is: what is a more intelligent way to combine 2 numbers before using them as keys of an object? I.E., how to combine 2 doubles into an unique Integer?
There is the definition of an array in JavaScript:
Array objects give special treatment to a certain class of property names. A property name P (in the form of a String value) is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 232 - 1. A property whose property name is an array index is also called an element. Every Array object has a length property whose value is always a nonnegative integer less than 232. The value of the length property is numerically greater than the name of every property whose name is an array index; whenever a property of an Array object is created or changed, other properties are adjusted as necessary to maintain this invariant. Specifically, whenever a property is added whose name is an array index, the length property is changed, if necessary, to be one more than the numeric value of that array index; and whenever the length property is changed, every property whose name is an array index whose value is not smaller than the new length is automatically deleted. This constraint applies only to own properties of an Array object and is unaffected by length or array index properties that may be inherited from its prototypes.
In other words, if the index you specify is a number representing an integer between 0 and 0xFFFFFFFE, then it is used as an array index. Any other value is taken as a string and it is used to create an object member instead of an array item.
So if you have constraints on your indices which would fit the valid range (0 to 0xFFFFFFFE) then you're good. Otherwise, what you have is probably the fastest.
So the following represents string indices which are members of object myHash:
myHash[x + "," + y] = z;
Someone mentioned using an array of arrays. That would not help you. You'd get many arrays instead of many strings. It would probably be about the same if not slower. The idea is something like this:
myHash[x] = []; // initialize the sub-array (must be done only once per value of 'x'
myHash[x][y] = z; // save z in that array
I do not recommend the double array because it will initialize one array for each value of 'x' on top of myHash and that probably not any faster than having the string concatenation (especially because you'll have to test whether the myHash[x] array was already defined or not...).
So... it is possible to write:
myHash[3.3] = "that worked?";
But if after that you check out the length, you'll notice it is zero:
console.log("Hash length = " + myHash.length);
This is because 3.3 is not an integer.
I'm writing a JavaScript interpreter for extremely resource-constrained embedded devices (http://www.espruino.com), and every time I think I have implemented some bit of JavaScript correctly I realise I am wrong.
My question now is about []. How would you implement one of the most basic bits of JavaScript correctly?
I've looked through the JavaScript spec and maybe I haven't found the right bit, but I can't find a useful answer.
I had previously assumed that you effectively had two 'maps' - one for integers, and one for strings. And the array length was the value of the highest integer plus one. However this seems wrong, according to jsconsole on chrome:
var a = [];
a[5] = 42;
a["5"]; // 42
a.length; // 6
but also:
var a = [];
a["5"] = 42;
a[5]; // 42
a.length; // 6
So... great - everything is converted into a string, and the highest valued string that represents an integer is used (plus one) to get the length? Wrong.
var a = [];
a["05"] = 42;
a.length; // 0
"05" is a valid integer - even in Octal. So why does it not affect the length?
Do you have to convert the string to an integer, and then check that when converted back to a string, it matches?
Does anyone have a reference to the exact algorithm used to store and get items in an array or object? It seems like it should be very simple, but it looks like it actually isn't!
As the specs said, and was noted by others:
"A property name P (in the form of a String value) is an array index if and only if ToString(ToUint32(P)) is equal to P and ToUint32(P) is not equal to 2^32-1."
That's explain why in your scenario "5" is considered an array index and "05" is not:
console.log("5" === String("5" >>> 0));
// true, "5" is equal to "5", so it's an index
console.log("05" === String("05" >>> 0));
// false, "05" is not equal to "5", so it's not an index
Note: the Zero-fill right shift is the shortest way in JS to have a substitute of ToUint32, shifting a number by zero.
See MDN
It's possible to quote the JavaScript array indexes as well (e.g.,
years["2"] instead of years[2]), although it's not necessary. The 2 in
years[2] eventually gets coerced into a string by the JavaScript
engine, anyway, through an implicit toString conversion. It is for
this reason that "2" and "02" would refer to two different slots on
the years object and the following example logs true:
console.log(years["2"] != years["02"]);
So with a["5"] you are accessing the array while a["05"] sets a property on the array object.
Arrays are just objects. That means they can have additional properties which are not considered elements of the array.
If the square bracket argument is an integer, it uses it to perform an assignment to the array. Otherwise, it treats it as a string and stores it as a property on the array object.
Edit based on delnan's comment and DCoder's comment, this is how JavaScript determines if it is an appropriate index for an array (versus just a property):
http://www.ecma-international.org/ecma-262/5.1/#sec-15.4
Arrays are also objects.
By doing this
a["05"] = 5;
You are doing the same thing as:
a.05 = 5;
However, the above will result in a syntax error, as a property specified after a dot cannot start with a number.
So if you do this:
a = [];
a["05"] = 5;
you still have an empty array, but the property of a named 05 has the value 5.
The number x is an array index if and only if ToString(ToUint32(x)) is equal to x (so in case of "05" that requirement is not met).
Can anyone explain why the second alert says 0 ?
var pollData = new Array();
pollData['pollType'] = 2;
alert(pollData['pollType']); // This prints 2
alert(pollData.length); // This prints 0 ??
The length of the array is only changed when you add numeric indexes. For example,
pollData["randomString"] = 23;
has no effect on length, but
var pollData = [];
pollData["45"] = "Hello";
pollData.length; // 46
changes the length to 46. Note that it doesn't matter if the key was a number or a string, as long as it is a numeric integer.
Besides, you are not supposed to use arrays in this manner. Consider it more of a side effect, since arrays are objects too, and in JavaScript any object can hold arbitrary keys as strings.
Because you haven't put anything into the array yet. You've only been assigning to a dynamically-created pollType attribute on the array object.
If you use numeric indices, then the array automagically takes care of length. For example:
var arr = [ ]; // same as new Array()
arr[2] = 'Banana!';
alert(arr.length); // prints 3 (indexes 0 through 2 were created)
The length property takes into consideration only those members of the array which names are indexes (like '1', '2', '3', ... ).
Arrays in JavaScript have numeric indexes only.
Use an object, which is essentially what you are doing above, setting properties on that array object.
array.length returns how many values are stored in the array. The first alert is returning the value of the position 'pollType'.
The reference guide I always use when needing help with javascript arrays is this page http://www.hunlock.com/blogs/Mastering_Javascript_Arrays
I'd also read what it says under the heading Javascript Does Not Support Associative Arrays, as you may run into problems with this also.
var pollData = Array();
function test() {
pollData[0] = 2
alert(pollData[0]);
alert(pollData.length);
}
//[x] is the array position; hence ['polltype'] is causing issues