Matching subscript from one array to another array

Question

I'm having this issue with arrays. Maybe I'm approaching this in a weird way, you guys let me know. I have two arrays:

String[] months = {"January","February","March","April","May",
                   "June","July","August","September",
                   "October","November","December"};
double[] rainfall ={4.22, 3.18, 3.03, 3.52, 4.54, 5.55, 
                    4.71, 4.35, 5.26, 5.46, 4.78, 4.09};

These numbers represent rainfall. I run the algorithm to find the Most and the Least from double[] rainfall, and it gives me the number 3.03, which is march. My question is, How can I correlate that subscript to the one from the array String[] months so that it shows me the name of the month as well? Should I make a stacked array instead?

In highlevel the idea should be, get the value from 'months' array based on the index of the output value in rainfall. Once you reply back with the language, we will be able to provide a possible solution. — JGV, Sep 19 '15 at 21:25

luboskrnac · Answer 1 · 2015-09-27T10:02:55.953

I suggest to change your data structure to map:

Map<String, Double> rainfallMap = new TreeMap<>();
rainfallMap.put("January", 4.22);
rainfallMap.put("February", 3.18);
rainfallMap.put("March", 3.03);
rainfallMap.put("April", 3.52);
rainfallMap.put("May", 4.54);
rainfallMap.put("June", 5.55);
rainfallMap.put("July", 4.71);
rainfallMap.put("August", 4.35);
rainfallMap.put("September", 5.26);
rainfallMap.put("October", 5.46);
rainfallMap.put("November", 4.78);
rainfallMap.put("December", 4.09);

Now you can do this (Java 8):

Entry<String, Double> minEntry = rainfallMap.entrySet().stream()
    .min((e1, e2) -> Double.compare(e1.getValue(), e2.getValue()))
    .get();

System.out.println(String.format("Minimal rainfall was %.2f in %s",
    minEntry.getValue(), minEntry.getKey()));

EDIT:

@Tagir Valeev suggested better retrieval of minimal entry:

Entry<String, Double> minEntry = 
    Collections.min(rainfallMap.entrySet(), Map.Entry.comparingByValue());

I compared both approached with JMH and @Tagir Valeev's suggestion is definitely better:

 Benchmark                          Mode  Cnt    Score    Error  Units
 Rainfall.getMinRaifallCollections  avgt    5   73.654 ±  3.768  ns/op
 Rainfall.getMinRainfallStreams     avgt    5  126.808 ± 10.559  ns/op

Good answer, though I'd suggest using LinkedHashMap or TreeMap so the iteration order is always the same. If two entries had the same value, a normal (undefined-order) HashMap could produce different answers when running this code multiple times. — dbort, Sep 19 '15 at 22:21
You don't need the Stream API here. Using simple `Entry minEntry = Collections.min(rainfallMap.entrySet(), Map.Entry.comparingByValue())` would yield the same result in shorter and more efficient way. Also you should not add [tag:java-stream] tag to the question if the problem *can* be solved via stream api unless the OP explicitly asked for such solution. It can be solved using tons of other APIs/libraries (Apache commons, Guava, etc.) should we add all of them to the tags? — Tagir Valeev, Sep 27 '15 at 03:58

score 0 · Answer 2 · answered Sep 19 '15 at 22:21

Well, you'll need a linear search to get the lowest value in the second array. When you find the lowest value, save its index. You'll use the index to find the corresponding month:

int minIndex = 0;

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

string month = months[minIndex];

faraza · Accepted Answer · 2015-09-22T00:43:02.550

-1

Pretty simple solution is to search for the index of your smallVal and bigVal.

for(int i = 0; i<rainfall.size(); i++){
   if(maxRain == rainFall[i])
         maxIndex = i;
   if(minRain == rainFall[i])
         minIndex = i;

}

smallMonth = months[minIndex];
bigMonth = months[maxIndex];

edited Sep 22 '15 at 00:43

answered Sep 19 '15 at 22:13

faraza

416
9
21

It's O(n) all the way. Also, the algorithm is wrong. – async Sep 20 '15 at 08:54
The algorithm is not wrong. He says in the question that given the max value and min value in the array, he wants to find their index. – faraza Nov 09 '15 at 09:23

Matching subscript from one array to another array

3 Answers3