Efficent way of dynamically filling an array with values from other array if condition x is matched-CodePudding

I am trying to get every value from the data array that is above my threshold, and put the values from data array that are above the threshold into a new array.

I found a way to do it but I am using two for loops, that are almost similar. So I am wondering if there is a way to do it without the two loops.

public int[] getValuesAboveThreshold(int threshold) {
        
        int counter = 0;
        int count =0;
        for (int i = 0; i < data.length;i  ) {
            if(data[i] > threshold) {
                counter  ;
            }
    }
        int [] thresholdArray = new int [counter];
        
        for(int i =0; i <data.length;i  ) {
            if(data[i] > threshold) {
                thresholdArray[count] = data[i];
                count  ;
            }
            
            
        }
        
        return thresholdArray;
                
    }

CodePudding user response：

You can do this very easily with a Stream:

public static void main(String[] args) {
  int threshold = 4;
  int[] data = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9 };
  int[] filteredArray = getValuesAboveThreshold(data, threshold);

  System.out.println(Arrays.toString(filteredArray));
}

private static int[] getValuesAboveThreshold(int[] originalArray, int threshold) {
  return Arrays.stream(originalArray)
      .filter(val -> val > threshold)
      .toArray();
}

CodePudding user response：

     public Collection<Integer> getValuesAboveThreshold(int threshold) {
        final Collection<Integer> datasWhichAreGreaterThanThreshold = new ArrayList<>();
        
        for (int i = 0; i < datas.length;i  ) {
            final int currentData = datas[i];
                    
            if(currentData > threshold) 
                datasWhichAreGreaterThanThreshold.add(currentData);
            
       }
        
       return datasWhichAreGreaterThanThreshold;
    }  
    
    public Integer[] getValuesAboveThreshold(int threshold) {
        final Collection<Integer> datasWhichAreGreaterThanThreshold = new ArrayList<>();
        
        for (int i = 0; i < datas.length;i  ) {
            final int currentData = datas[i];
                    
            if(currentData > threshold) 
                datasWhichAreGreaterThanThreshold.add(currentData);
            
       }
        
        
        return datasWhichAreGreaterThanThreshold.toArray(Integer[]::new);
    }

NOTE: Your solution does not contain inner loops. Hence, the complexity is Q(n) already. [no matter how many other loops are used] -- performance would be approximately same with exactly one loop solution for large number of datas.