Javascript syntax Help on sorting function

Question

Code

function SortByID(x,y) {
    return x.id - y.id;
}

function SortByName(x,y) {
    return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));
}

Problem Description

I am new to Javascript and I am learning how to make a sorting algorithm. I have a few questions regarding the two functions above.

1.Can you please explain the line of code below to me in words?

return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));

2.What does the question mark in the above code mean?

3.what doest the "? 1: -1" and "? 0 :" means?

Many Thanks!

Seth · Accepted Answer · 2012-01-19 15:40:09Z

4

You are looking at a ternary operator. It's a short way of writing if else statements.

((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));

Is the same thing as.

if ( x.Name == y.Name ) {
    return 0;
} else {
    if ( x.Name > y.Name ) {
        return 1;
    } else {
        return -1;
    }
}

Another way to read it would be like this.

(( Condition ) [IF TRUE] 0 [IF FALSE] (( Condition ) [IF TRUE] 1 [IF FALSE] -1 ));

answered Jan 19, 2012 at 15:40

Seth

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2 Comments

s4y Over a year ago

It’s not exactly like an if statement — it’s important to understand that t ternary operator evaluates to a value — so you can use it anywhere, even when you’re not returning something.

Seth Over a year ago

This is very true. However, you have to return them to something whether it's a variable or return statement...which was confusing at first. It definitely takes some time to get used to.

Rich O'Kelly · Accepted Answer · 2012-01-19 15:44:06Z

1

The question mark is known as the conditional operator (or ternary operator) it is a shorthand way of an if then else block, bearing this in mind we have:

1.Can you please explain the line of code below to me in words?

If x.Name equals y.Name return 0 otherwise if x.Name is greater than y.Name return 1 otherwise return -1

2.What does the question mark in the above code mean?

The '?' operator takes the form:

(expression evaluating to true / false) ? (if true expression) : (if false expression)

3.what doest the "? 1: -1" and "? 0 :" means?

See answer 2 for syntactic meaning. In this context returning 0 means the values are deemed equal, -1 means the first value is less than the second and 1 means that the first value is greater than the second.

edited Jan 19, 2012 at 15:44

answered Jan 19, 2012 at 15:38

Rich O'Kelly

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1 Comment

Evan Davis Over a year ago

check your final return; should be -1 not 0

AlexZam · Accepted Answer · 2012-01-19 15:50:04Z

1

1 . That means literally:

    if(x.Name == y.Name) return 0;
    else{
      if (x.Name > y.Name) return 1;
      else return -1;
    }

2. and 3. The key is in ternary operator syntax. Expression A ? B : C means "check if A is true and if it is true then expression value is B otherwise C"

answered Jan 19, 2012 at 15:50

AlexZam

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Comments

ek_ny · Accepted Answer · 2012-01-19 15:39:19Z

0

Sorting function which explains how two items will be sorted when compared to eachother

a return value of greater than one will flip the order of the items

part of the ternary operator
part of the ternary operator

answered Jan 19, 2012 at 15:39

ek_ny

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Comments

VirtualTroll · Accepted Answer · 2012-01-19 15:41:58Z

0

This type of statement is found in other programming language. It is shorter version of the if else statement. For example

if(condition){
statement1} else {
statement2}

can be written as

condition ? statment1 : statement2

In your case, two condition are being tested and the equivalent if else statement would be

    if(x.Name == y.Name) {
    return 0;
} else {
     if(x.Name > y.Name){
    return 1;}
    else {
    return -1;}
    }

answered Jan 19, 2012 at 15:41

VirtualTroll

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Comments

Evan Davis · Accepted Answer · 2012-01-19 15:42:18Z

0

return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));

If x.Name is the same as y.Name, return 0; otherwise, if x.Name is greater than y.Name, return 1; if both those statements are false, finally return -1.

Bonus note: use === instead of == so that you compare both type and value, not just value.

answered Jan 19, 2012 at 15:42

Evan Davis

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Comments

Alex Turpin · Accepted Answer · 2012-01-19 15:42:44Z

This makes heavy use of the ternary operator. The ternary operator is like a if statement in one line.

expression ? result if true : result if false

So that

3 == 3 ? "yes" : "no"

Returns "yes". Now basically this is a sort function. Sort functions want you to give them a number that represents a comparison between two items. If the items are equivalent, you return 0. If not, you return 1 or -1 to determine which one is bigger.

This expression basically checks if the names are equal. If they are, it returns zero. Otherwise, there is another condition which will return 1 if x.Name is "bigger" than y.Name, or -1 otherwise.

This could be expressed as the following:

if (x.Name == y.Name) {
    return 0;
}
else {
    if (x.Name > y.Name) {
        return 1;
    }
    else {
        return -1;
    }
}

Emmanuel N · Accepted Answer · 2012-01-19 15:43:30Z

0

  return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));

In other words

 if(x.Name == y.Name){
      return 0;
 }
 else{
    if(x.Name > y.Name){
        return 1;
    }
    else{
        return -1;
     }   
 }

answered Jan 19, 2012 at 15:43

Emmanuel N

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Comments

Chris Yeung · Accepted Answer · 2012-01-24 16:36:46Z

I found a good site to explain these syntax :) Sorting Tutorial

Thanks for the answers above.

These functions are for the Javascript's inbuilt .sort() function to sort accordingly.

if you have:

var obj_to_sort; //in json format

Then we can simply sort this variable by entering:

obj_to_sort.sort(SortByName); //or
obj_to_sort.sort(SortByID); ...etc

and for each SortByXX function (which is declared by yourself), it should take in two parameters like below:

function SortByID(x,y) {
        return x.id - y.id;
}

function SortByName(x,y) {
    return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));
}

There are three scenarios:

if -1(or neg) is returned, x will come before y;

if 1(or pos) is returned, x will come after y;

if 0 is returned, x = y;

And by using .sort() function, it will automatically sort according to your algorithm.

and for:

 return ((x.Name == y.Name) ? 0 : ((x.Name > y.Name)? 1: -1));

it means:

if x = y ; output 0
otherwise, if x > y ; output 1
otherwise, output -1.

? means output, : means otherwise.

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