Best way to retrieve variables from Expressions?

[ezylang]

Best way to retrieve variables from Expressions?

[fobbyal]

@Kilosh

I have a working solution here.. it is not pretty but it works and also you need java 8 for this.

    private static final Set<String> defaultVariables;
    private static final Set<String> defaultOperators;

    static {
        TreeSet<String> defaults = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
        Expression exp = new Expression("1+1");
        defaults.addAll(exp.getDeclaredFunctions());
        //defaults.addAll(exp.getDeclaredOperators());
        defaults.addAll(exp.getDeclaredVariables());
        defaultVariables = Collections.unmodifiableSet(defaults);
        defaultOperators = exp.getDeclaredOperators();
    }

    public static Set<String> parseForVars(String formulaExpression) {
        formulaExpression = replaceFunctions(formulaExpression, defaultVariables);
        formulaExpression = replaceOperators(formulaExpression, defaultOperators);
        log.debug("transformed {}", formulaExpression);
        formulaExpression = formulaExpression.replace('(', ',');
        formulaExpression = formulaExpression.replace(')', ',');
        formulaExpression = formulaExpression.replaceAll("\\s+", ",");
        log.debug("formulaExpression {}", formulaExpression);
        return Collections.unmodifiableSet(
                Stream.of(formulaExpression.split(","))
                        .map(String::trim)
                        .filter(v -> !v.matches("-?\\d+(.\\d+)?"))
                        //.filter(v -> !v.matches("\\w+"))
                        .filter(v -> v.length() != 0)
                        .collect(Collectors.toCollection(() -> new TreeSet<>(String.CASE_INSENSITIVE_ORDER))));
    }

    public static String replaceFunctions(String str, Set<String> val) {
        for (String op : val) {
            str = str.replaceAll("(?i)\\b" + Pattern.quote(op) + "\\b", ",");
        }
        return str;
    }

    public static String replaceOperators(String str, Set<String> val) {
        for (String op : val) {
            str = str.replace(op, ",");
        }
        return str;
    }

[uklimaschewski]

This should be very easy to implement, simply extract anything that is not a function, operator, (, ), , or a constant number:

    public List<String> getUsedVariables() {
        List<String> result = new ArrayList<String>();
        Tokenizer tokenizer = new Tokenizer(expression);
        while (tokenizer.hasNext()) {
            String token = tokenizer.next();
            if (functions.containsKey(token) || operators.containsKey(token)
                    || token.equals("(") || token.equals(")")
                    || token.equals(",") || isNumber(token)) {
                continue;
            }
            result.add(token);
        }
        return result;
    }

[Kilosh]

Thanks. Took your implementation. You are missing to check on the constants "PI", "TRUE", and "FALSE".

[uklimaschewski]

I implemented the function in commit b35f03c