The Python collections modules' counter in Java

• Generic counter class can count items of any data type.

  • (Note: This is *NOT* the same as counting items of different types in the same counter. One counter instance can count items of only 1 type. But that type can be whatever you want.)

• Initialization from arrays and iterables(Lists and Sets).

  • The Python counter supports this type of initialization so why shouldn't we.

• Initialization from a Map of values.

  • The Python counter supports initialization from a dictionary where keys are items and values are counts.
  • So we have an overload that accepts a Map<I,Integer>, where I is the type of the items being counted. The values are the counts of those items.

• Initialization from another counter.

• Finding the intersection and union of two counters counting the same type of item.

  • These methods conform to the reference Python implementation given in the repo.

• Data extraction as a HashMap.

  • There is a method for getting the data of the counter as a HashMap of item-frequency pairs.
  • This can be useful if you have existing code that deals with Maps.

• Iteration.

  • This implementation provides an iterator for iterating over the items of the counter. The order of the items can be set accordingly.
  • The iterator is read-only and hence cannot be used to modify the counter.

• Printing.

  • An override for 'toString()' has been provided for convenience.

import ilvanip.Counter;
String[]strings="ISE MSE ESE TOT ISE MSE ESE TOT ISE".split(" ");
//Initialzing a counter of strings from an array of strings.
Counter<String>c=new Counter<String>(strings);
System.out.println(c);

• Statistical operations are unavailable on this Counter.

  • As iterators have been provided, you can implement your own.

• A counter is essentially a Map of sorts. But this implementation is not fully compatible with the Collections Framework as it is not a Map(it doesn't extend AbstractMap). As a result, it cannot be used as an argument to functions that expect a Map as an argument.

  • You can take the Map view of the counter and work on it from there.
  • Once done, you can create a new counter from the modified Map.