Find the mode (most frequent value in an array) using a simple for loop?

问题

How do I find the mode (most frequent value in an array) using a simple for loop?

The code compiles with a wrong output.

Here is what I have:

public static void mode(double [] arr)
{
    double mode=arr[0];

    for(int i = 1; i<arr.length; i++)
    {   
        if(mode==arr[i])
        {
            mode++;
        }

     }


    return mode;
}

回答1:

First I sort the array by order and then I count occurrences of one number. No hashmaps only for loop and if statements.

My code:

static int Mode(int[] n){
    int t = 0;
    for(int i=0; i<n.length; i++){
        for(int j=1; j<n.length-i; j++){
            if(n[j-1] > n[j]){
                t = n[j-1];
                n[j-1] = n[j];
                n[j] = t;
            }
        }
    }

    int mode = n[0];
    int temp = 1;
    int temp2 = 1;
    for(int i=1;i<n.length;i++){
        if(n[i-1] == n[i]){
            temp++;
        }
        else {
            temp = 1;
        }
        if(temp >= temp2){
            mode = n[i];
            temp2 = temp;
        }
    }
    return mode;
}

回答2:

-Just use a HashMap which contains the array index values as the keys and their occurrence numbers as the values.

-Update the HashMap as you traverse the for loop by checking to see if the current index already exists in the HashMap. IF IT DOES then find that double in the hash map and see how many times it has already occurred and put it back in the HashMap with one more occurrence.

-I did it in Java because that's what it looks like you are using. What's also good is that the time complexity is O(n) which is the best you could possibly get for this type of scenario because you have to visit every element at least once.

-So if you have an array like this of doubles: { 1,2,3,1,1,1,5,5,5,7,7,7,7,7,7,7,7,7} Then the hash map will look something like this at the end: { 1->4, 2->1, 3->1, 5->3, 7->9 } Meaning that "1 occurred 4 times, 2 occured 1 time .... 7 occurred 9 times" etc.

    public static double mode(double [] arr)
    {
        HashMap arrayVals = new HashMap();
        int maxOccurences = 1;
        double mode = arr[0];

        for(int i = 0; i<arr.length; i++)
        {   
            double currentIndexVal = arr[i];
            if(arrayVals.containsKey(currentIndexVal)){
                int currentOccurencesNum = (Integer) arrayVals.get(currentIndexVal);
                currentOccurencesNum++;
                arrayVals.put(currentIndexVal, currentOccurencesNum );
                if(currentOccurencesNum >= maxOccurences)
                {
                    mode = currentIndexVal;
                    maxOccurences = currentOccurencesNum;
                }
            }
            else{
                arrayVals.put(arr[i], 1);
            }
        }


        return mode;
    }

回答3:

This code is a different way that does not use hashmaps. This method, created in java, takes an array as the parameter and creates another array called "numberCount" within the method. This array "numberCount" will set its index to the value in the array. The index of "numberCount"that contains the value in the array passed will add 1 to the value of "numberCount" ("++numberCount[array[i]]") then will go to the next value in the array (repeat until the end of the array). Then creates another for loop to go through each value of the array in "numberCount", which ever index has the highest value/count will be stored and return as "max." This method will have to undergo some difficult changes to use a double array. but seems to work great with an int array.

public static int findMostFrequentValue(int[] array) {
    int i;
    int[] numberCount = new int[100];
    for (i = 0; i < array.length; i++)++numberCount[array[i]];
    int max = 0;
    int j;

    for (j = 0; j < numberCount.length; j++) {
        if (numberCount[j] > max) max = j;
    }
    return max;
}

回答4:

You should check the number of occurances of every element in your array. You can do it by comparing every element of array with herself and others via 2 inner for loops.

Remember, if the array is not sorted and contains more then 1 modal value (thus repeating number of occurances) this will return the first one. It maybe wise to order the array first by Arrays.sort(array) so that you can pick the smallest or biggest modal value.

public static int modeOfArray(int[] array){
    int mode;     
    int maxOccurance = 0;

    for(int i=0; i<array.length; i++){
        int occuranceOfThisValue = 0;
        for(int j=0; j<array.length; j++){
            if(array[i] == array[j])
               occuranceOfThisValue++;
        }

        if(occuranceOfThisValue > maxOccurance){
            maxOccurance = occuranceOfThisValue;
            mode = array[i];
        }
    }
    return mode;
}

来源：https://stackoverflow.com/questions/7141723/find-the-mode-most-frequent-value-in-an-array-using-a-simple-for-loop