Replace a map of values in string

Question

Let's say I have a String text = "abc" and I want to replace a map of values, eg:

a->b
b->c
c->a

How would you go for it?

Because obviously:

map.entrySet().forEach(el -> text = text.replaceAll(el.getKey(), el.getValue()))

won't work, since the second replacement will overwrite also the first replacement (and at the end you won't get bca)

So how would you avoid this "replacement of the previous replacement"?

I saw this answer but I hope in a more concise and naive solution (and hopefully without the use of Apache external packages)

By the way the string can be also more than one character

(and at the end you won't get cba) >> Did you mean `bca` for `abc`? — Pubudu Sitinamaluwa, Jul 14 '21 at 18:01
If the map is string to string, the "replace" operations are order dependant. Is the map a [`NavigableMap`](https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/util/NavigableMap.html)? If not, how to order determined? — Bohemian, Jul 15 '21 at 00:20
@Bohemian good point... the order it's not relevant for the sake of the example (but yes, it's order dependent).. you might think like a `List>`, so there order is the position of the pair in the list — Alberto Sinigaglia, Jul 15 '21 at 08:40

score 0 · Answer 1 · answered Jul 14 '21 at 17:58

0

I came up with this solution with java streams.

String text = "abc";
Map<String, String> replaceMap = new HashMap<>();
replaceMap.put("a", "b");
replaceMap.put("b", "c");
replaceMap.put("c", "a");

System.out.println("Text = " + text);

text = Arrays.stream(text.split("")).map(x -> {
    String replacement = replaceMap.get(x);
    if (replacement != null) {
        return x.replace(x, replacement);
    } else {
        return x;
    }
}).collect(Collectors.joining(""));

System.out.println("Processed Text = " + text);

Output

Text = abc
Processed Text = bca

answered Jul 14 '21 at 17:58

Pubudu Sitinamaluwa

958
7
21

This doesn't look like it would handle cases where the string to replace is longer than one character (because it uses `text.split("")`). – Green Cloak Guy Jul 14 '21 at 18:18
Yes. The PO did not mention that he wanted to map words. I crafted this answer to go with the given requirement. – Pubudu Sitinamaluwa Jul 14 '21 at 18:23
hi, thanks for the answer, but this works only for the example, but a string can be also longer than one character – Alberto Sinigaglia Jul 14 '21 at 23:42

Green Cloak Guy · Answer 2 · 2021-07-14T18:28:32.207

This is a problem I'd normal handle with regex replacement. The code for that in Java is a bit verbose, but this should work:

String text = "abc";
Map<String, String> map = new HashMap<>();
map.put("a", "b");
map.put("b", "c");
map.put("c", "a");

String regex = map.keySet()
                  .stream()
                  .map(s -> Pattern.quote(s))
                  .collect(Collectors.joining("|"));

String output = Pattern.compile(regex)
                       .matcher(text)
                       .replaceAll((m) -> {
                           String s = m.group();
                           String r = map.get(s);
                           return r != null ? r : s;
                       });
System.out.println(output); 
// bca

It's relatively straightforward, if a little verbose because Java. First, create a regex expression that will accept any of the keys in the map (using Pattern.quote() to sanitize them), and then use lambda replacement to pluck the appropriate replacement from the map whenever an instance is found.

The performance-intensive part is just compiling the regex in the first place; the replacement itself should make only one pass through the string.

Should be compatible with Java 1.9+

SomeDude · Answer 3 · 2021-07-14T18:44:03.990

0

Java 8 onwards, there is a method called chars that returns an IntStream from which you can get a character corresponding to integer represented by the character and map it using your map.

If your map is String to String map then you could use:

text = text.chars().mapToObj(el -> map.get(String.valueOf((char)el))).
                                                 collect(Collectors.joining(""));

if your map is Character to Character then just remove String.valueOf()

text = text.chars().mapToObj(el -> map.get((char)el)).collect(Collectors.joining(""));

edited Jul 14 '21 at 18:44

answered Jul 14 '21 at 18:39

SomeDude

13,876
5
21
44

hi, thanks for the answer and for your time, but this works only for the example, but a string can be also longer than one character – Alberto Sinigaglia Jul 14 '21 at 23:45

Replace a map of values in string

3 Answers3