Styjun

I have an ArrayList<String[]> which contains the following data:

[Branford, Paddock Lane, 136, 1]
[Branford, Paddock Lane, 42, 3]
[Branford, Hartford Road, 117, 0]
[Branford, Hartford Road, 45, 3]
[McAlister, Sigourney Street, 103, 3]
[McAlister, Sigourney Street, 61, 1]
[McAlister, Stanford Street, 1, 3]
[McAlister, Stanford Street, 34, 4]
[Cypress Gardens, Route 115, 112, 12]
[Cypress Gardens, Park Road, 10, 4]
[Cypress Gardens, Park Road, 49, 4]
[Cypress Gardens, Old Farm Road, 28, 5]
[Cypress Gardens, Old Farm Road, 79, 3]
[Germfask, Exeter Court, 28, 7]
[Germfask, South Boulevard, 119, 6]
[Germfask, South Boulevard, 135, 3]
[Minford, Liberty Lane, 41, 3]
[Minford, Liberty Lane, 52, 4]
[Minford, State Street West, 103, 0]

The first element from each array of strings is a city's name and the last element is a counter. I need to extract data which will contain also array of strings but only with one city name and the largest counter. For example, for Branford the result will be [Branford, Paddock Lane, 42, 3]. How can I extract this data only with forEach loops?
Thank you.

I have tried by using a forEach through the ArrayList and comparing each counter from current element with the next one where the city name is the same.

The output is not as expected, as it contains no data.

final int[] max = Integer.parseInt(arrayListSrc.get(0)[3]);
ArrayList<String[]> arrayList = new ArrayList<>(1);
final int[] index = 0;
arrayListSrc.forEach(strings -> 
 if (strings[0].equals(arrayListSrc.get(index[0])[0])) 
 if (Integer.parseInt(strings[3]) < Integer.parseInt(arrayListSrc.get(index[0])[3])) 
 if (Integer.parseInt(arrayListSrc.get(index[0])[3]) > max[0]) 
 max[0] = Integer.parseInt(arrayListSrc.get(index[0])[3]);
 arrayList.add(strings);
 
 
 
 index[0]++;
);

I had something like this:

Map<String, String[]> result = new TreeMap<>();


for(String[] s : source) 
 if(!result.containsKey(s[0]))
 result.put(s[0], s);
 else if (Integer.valueOf(result.get(s[0])[3]) < Integer.valueOf(s[3])) 
 result.put(s[0], s);
 


for(String k : result.keySet()) 
 System.out.println(k + ": " + Arrays.toString(result.get(k)));

This should print:

Branford: [Branford, Paddock Lane, 42, 3]
Cypress Gardens: [Cypress Gardens, Route 115, 112, 12]
Germfask: [Germfask, Exeter Court, 28, 7]
McAlister: [McAlister, Stanford Street, 34, 4]
Minford: [Minford, Liberty Lane, 52, 4]

Is that the result you are after? You do have the challenge that you have entries with the same number of hits.

First of all, try to map your String[] to a suitable data structure next time, since it will be a lot easier to handle. Just create a suitable class, thats what object oriented programming is for.

But, to answer the question, you can map the plain List<String[]> in the following way:

Map<String, String[]> results = source.stream().collect(
 Collectors.toMap(s -> s[0], Function.identity(),
 BinaryOperator.maxBy(
 Comparator.comparing(s -> Integer.valueOf(s[3])))));

The result is a Map where the key represents the city name and the value is the original String[] maxed by the counter. This solution does not require the use of forEach(), but rather stream operations to achieve the expected result.

You can, however, use forEach() to print or further operate on the results:

results.forEach((s, strings) -> 
 System.out.println(s + " " + Arrays.toString(strings));
);