How can I split the string like
"-3.0*6.7+(5/2)*-0.8--12.98+4^-0.5"
by using regex expression to
-3.0,*,6.7,+,(,5,/,2,),*,-0.8,-,-12.98,+,4,^,-0.5
-
@KennyTM 4,-,3 but if it was "4--3" then 4,-,-3Alaattin KAYRAK– Alaattin KAYRAK2011-05-07 16:04:00 +00:00Commented May 7, 2011 at 16:04
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2 Answers
It is impractical to use regex for this task: you'd better create some sort of tokenizer/lexer to create tokens from your input source. Especially the unary minus signs make this hard for a regex split.
But to answer you question, you could split on the following pattern:
(?=[+*/()^])|(?<=[+*/()^])|(?<=\d-)|(?<=\d)(?=-)
which means:
# Split on:
(?=[+*/()^]) # the empty space that has one of: +, *, /, (, ), ^ ahead of it
| # OR
(?<=[+*/()^]) # the empty space that has one of: +, *, /, (, ), ^ before it
| # OR
(?<=\d-) # the empty space that has a digit followed by a minus sign before it
| # OR
(?<=\d)(?=-) # the empty space that has a digit before it and a minus sign ahead of it
Comments
I am assuming you ultimately want to evaluate this expression. Here's a code that evaluates arithmetic expressions. It supports the basic arithmetic operators over integers + parenthesis. It should be quite easy to adapt it to support floating point literals.
public class CompactSolver {
private String input;
public CompactSolver(String input_) {
input = input_.trim();
}
private char peek(int offset) {
return offset >= input.length() ? '\0' :
input.charAt(offset);
}
private boolean consumeIf(char c) {
if (peek(0) != c)
return false;
consume(1);
return true;
}
private String consume(int numChars) {
if (numChars == 0)
throw new RuntimeException("syntax error");
String result = input.substring(0, numChars);
input = input.substring(numChars).trim();
return result;
}
public double eval() {
double lhs = mul();
if (consumeIf('+'))
return lhs + eval();
else if (consumeIf('-'))
return lhs - eval();
return lhs;
}
private double mul() {
double lhs = unary();
if (consumeIf('*'))
return lhs * mul();
else if (consumeIf('/'))
return lhs / mul();
return lhs;
}
private double unary() {
if (consumeIf('-'))
return -unary();
if (consumeIf('(')) {
double result = eval();
if (!consumeIf(')'))
throw new RuntimeException("Missing ')'");
return result;
}
return literal();
}
private double literal() {
for (int i = 0; true; ++i)
if (!Character.isDigit(peek(i)))
return Integer.parseInt(consume(i));
}
}
