Delete occurrence of an element is it occurs more than n times

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I would need to erase the value if it exceeds the number of n, for example:

JavaScript

sortN([2, 3, 3, 3, 4, 4], 1);-> [2, 3, 4]

In other words, the number of occurrences should not exceed n. I have been trying tackle this problem with different approaches but still can`t get the desired output

What I have tried:

The closest I got was to count number of occurrences of every element, like this:

JavaScript

function compressArray(original) {
 
	var compressed = [];
	// make a copy of the input array
	var copy = original.slice(0);
 
	// first loop goes over every element
	for (var i = 0; i < original.length; i++) {
 
		var myCount = 0;	
		// loop over every element in the copy and see if it's the same
		for (var w = 0; w < copy.length; w++) {
			if (original[i] == copy[w]) {
				
				myCount++;
				
				delete copy[w];
			}
		}
 
		if (myCount > 0) {
		
			compressed.push(original[i], myCount);
		}
	}
 
	return compressed;
};

Is this really useful? Should I take a different approach?

Posted 10-Aug-16 4:22am

AlexLearne

Updated 10-Aug-16 4:51am

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Richard Deeming · Accepted Answer · 2016-08-10T04:51:00

Solution 1

How about something like this:

JavaScript

function compressArray(original, maxOccurrences) {
    if (!original) { return null; }
    if (maxOccurrences < 1) { return []; }
    
    var result = [];
    var itemCounts = {};
    for (var index = 0; index < original.length; index++){
        var item = original[index];
        var count = itemCounts[item] || 0;
        if (count < maxOccurrences) {
            result.push(item);
            itemCounts[item] = count + 1;
        }
    }
    
    return result;
}

Demo[^]

Posted 10-Aug-16 4:51am

Richard Deeming

Comments

AlexLearne 10-Aug-16 11:05am

Thank you a lot! But since I am a newbie I have some questions to ask.Would you please help me understand the code completely?
What is this line doing? var count = itemCounts[item] || 0;
Are you adding the values to the object?
Thanks anyway!

Richard Deeming 10-Aug-16 11:13am

It's a shorthand way of writing:

var count = itemCounts[item];
if (count === undefined) {
   count = 0;
}

When we encounter an item we haven't seen before, the itemCounts object doesn't contain a value for that item, so itemCounts[item] returns undefined. In that case, we want count to be set to 0, since we haven't seen that item yet.

Within the if block, we then store count + 1 against the item in the itemCounts object. This will add a new value if the key doesn't exist yet, or update the existing value if it does exist.

AlexLearne 10-Aug-16 11:17am

Thanks! Great help!

Delete occurrence of an element is it occurs more than n times

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Delete occurrence of an element is it occurs more than n times

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