Extracting token from a string

Question

I've a some strings like that "paddington road" and I need to extract the word "road" from this string. How can I do that?

The problem is that I need to process a list of streets and extract some words like "road" "park" "street" "boulevard" and many others.

What could be the best way to do that? The complexity is O(n*m) and if you consider that I process more than 5000 streets, the performance should be very important.

I'm extracting the values from a Postgres db and putting into a List but I'm not sure it's the best way, may be a hash table is faster to query?

I tried something like this:

    // Parse selectedList
    Iterator<String> it = streets.iterator();
    Iterator<String> it_exception = exception.iterator();

    int counter = streets.size();
    while(it.hasNext()) {   

        while ( it_exception.hasNext() ) {
            // remove substring it_exception.next() from it.next()              
        }               
    }

What do you think?

Answer 1

You can try Set:

Set<String> exceptions = new HashSet<String>(...);
for (String street : streets) {
    String[] words = street.split(" ");
    StringBuilder res = new StringBuilder();
    for (String word : words) {
        if (!exceptions.contains(word)) {
            res.append(word).append(" ");
        }
    } 
    System.out.println(res);
}

I think complexity will be O(n), where n is a number of all words in streets.

Answer 2

You need to get a new iterator for your list of keywords at each iteration of the outer loop. The easiest way is to use the foreach syntax:

for (String streetName : streets) {
    for (String keyword : keywords) {
        // find if the string contains the keyword, and perhaps break if found to avoid searching for the other keywords
    }
}

Don't preoptimize. 5000 is nothing for a computer, and street names are short strings. And if you place the most frequent keywords (street, rather than boulevard) at the beginning of the keyword list, you'll have less iterations.

Answer 3

List streets = new ArrayList<String>();
    streets.add("paddington road");
    streets.add("paddington park");

    for (Object object : streets) {
        String cmpstring = object.toString();
        String[] abc = cmpstring.split(" ");
        String secondwrd = abc[1];
        System.out.println("secondwrd"+secondwrd);

    }

you can keep secondwrd in a list or string buffer etc....