Convert String to HashMap/MultiSet?

Question

What is the best way to convert a long string to a data structure with words and counts.

I would do .split(" ") to split on spaces and presumably make an arraylist, then maybe go through arraylist and add each item to a hashmap or multiset? I'm not sure what the best way to do this is/if it can be done directly with some sort of hashmap without making an arraylist first.

Thanks!

just lots and lots of strings, something like "word bla bla word another word /moren+!*&^@#random words"? — LemonMan, Jun 28 '13 at 19:15
How do you define 'best'? as fast as possible, use as little memory as possible or easy to read and understand the code? — Simon Forsberg, Jun 28 '13 at 19:15
well i'm not too concerned about it being optimal any acceptable way is good? I'm just not sure what people usually do for such a common task. likely i'll make arraylist, then go through arraylist and add each item to hashmap with a count? then merge multiple hashmaps for different strings — LemonMan, Jun 28 '13 at 19:17

score 3 · Answer 1 · answered Jun 28 '13 at 19:22

3

If you're referring to a Guava Multiset, this is just the one line

HashMultiset.create(
  Splitter.on(CharMatcher.WHITESPACE).omitEmptyStrings()
    .split(string));

answered Jun 28 '13 at 19:22

Louis Wasserman

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interesting, this looks quite simple, though I may go with the other case to avoid a situation where someone using my code won't have guava – LemonMan Jun 28 '13 at 19:26

Davey Chu · Accepted Answer · 2013-06-28T20:35:20.947

1

import java.util.HashMap;
import java.util.Map;

public class Test {
    private static Map<String, Integer> count = new HashMap<String, Integer>();

    public static void main(String[] args) {
        addToCountMap("This is my test string and it contains Test and test and string and some more");
        addToCountMap("This is my test string and it contains Test and test and string and some more");
        addToCountMap("This is my test string and it contains Test and test and string and some more");
        addToCountMap("This is my test string and it contains Test and test and string and some more");
        addToCountMap("This is my test string and it contains Test and test and string and some more");

        mergeWithCountMap(count);

        System.out.println(count);
    }

    private static void addToCountMap(String test) {
        String[] split = test.split(" ");
        for (String string : split) {
            if (!count.containsKey(string)) {
                count.put(string, 0);
            }
            count.put(string, count.get(string) + 1);
        }
    }

    private static void mergeWithCountMap(Map<String, Integer> mapToMerge) {
        for (String string : mapToMerge.keySet()) {
            if (!count.containsKey(string)) {
                count.put(string, 0);
            }
            count.put(string, count.get(string) + mapToMerge.get(string));
        }
    }
}

edited Jun 28 '13 at 20:35

answered Jun 28 '13 at 19:17

Davey Chu

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count.put(sting, 1) if you want the actual number in count. – stark Jun 28 '13 at 19:19
yup, that looks like what I want. My only followup question would be, how would I merge two hashmaps? I may need to do this for hashmaps from different sources – LemonMan Jun 28 '13 at 19:19
uh what do you mean, i'm not sure, i want the total number of occurences, so i guess we need to add 1 to the existing count? – LemonMan Jun 28 '13 at 19:20
When you find the first occurrence, you want to start the count at 1. – stark Jun 28 '13 at 19:23
oh that line yup you'd put 1 – LemonMan Jun 28 '13 at 19:24
@stark the first occurence is started at 1 in my example. – Davey Chu Jun 28 '13 at 19:24
@daveychu - sorry. I assumed an 'else' for the increment but I see you don't have one. – stark Jun 28 '13 at 19:41
thanks! that's quite helpful. but in some cases, what would be the best way of combining two maps (if I already have something in map form rather than string form) – LemonMan Jun 28 '13 at 20:30
1

@Lemonio added merge example. – Davey Chu Jun 28 '13 at 20:35

Convert String to HashMap/MultiSet?

2 Answers2