how to iterate over specific elements in string objects (arraylist Java)

Question

ArrayList<String> dnaArray = new ArrayList<>();
ArrayList<Character> compArray = new ArrayList<Character>();

// [tac, tat, tta, aaa, aac, aca, aac, ttt]

public void createCompliment() {
    for (String letters : dnaArray) {
        for (int i = 0, len = letters.length(); i < len; i++) {
            char character = letters.charAt(i);
            if (character == 'a'){
                character = 't';
            } else if (character == 'c') {
                character = 'g';
            }
            compArray.add(character);
        }
    }
}

How would I access specific characters, change 'a' to 't' and similarily from 'c' to 'g'. Then added to a new arraylist and return something like:

[ttg, ttt, ttt, ttt, ttg, tgt, ttg, ttt]

instead of: [t, t, g, t, t, t, t, t, t, t, t, t, t, t, g, t, g, t, t, t, g, t, t, t]

appreciate it

collect into another list and wrap it up once it hits the desired size, add it to the outer list then. so some kind of inner.add(foo) and then if (inner.size() > desired) you do outer.add(inner) and inner = new ArrayList<>() as preparation for the next batch. — Zabuzard
– Zabuzard, Commented Aug 14, 2020 at 9:37

Carlo Moretti · Accepted Answer · 2020-08-14 09:43:52Z

1

the easiest way in my opinion is to use string replace:

ArrayList<String> dnaArray = new ArrayList<>();
ArrayList<String> compArray = new ArrayList<String>();

public void createCompliment() {
    for (String letters : dnaArray) {
        compArray.add(letters.replace('a', 't').replace('c', 'g'));
    }
}

answered Aug 14, 2020 at 9:43

Carlo Moretti

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2 Comments

Abhishek Chauhan Over a year ago

This would work well but will Java optimise it to do it in one traverse.

Carlo Moretti Over a year ago

@AbhishekChauhan you're right, this does 2 traverses. With the given inputs I don't think complexity is an issue.

Hulya · Accepted Answer · 2020-08-14 09:45:59Z

1

You can use a StringBuilder() to create the new String then add it to compArray.

Try this:

for(String letters : dnaArray) {
    StringBuilder sb = new StringBuilder();
    for(int i=0; i<letters.length(); i++) {
        char character = letters.charAt(i);
        if (character == 'a'){
            sb.append("t");
        }
        else if (character == 'c'){
            sb.append("g");
        } else {
            sb.append(String.valueOf(character));
        }
    }
    compArray.add(sb.toString());
}

Output:

[ttg, ttt, ttt, ttt, ttg, tgt, ttg, ttt]

answered Aug 14, 2020 at 9:45

Hulya

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