How to Extract Double Values from Strings Using Regex?

Extraction of Floating-Point Values from Strings Using Regex

Question: How can a regex be used to isolate a double value from a string?

Solution:

To extract a double value from a string using regex, a sophisticated regexp can be used, such as:

<code class="python">import re
re_float = re.compile("""(?x)
   ^
      [+-]?\ *      # first, match an optional sign *and space*
      (             # then match integers or f.p. mantissas:
          \d+       # start out with a ...
          (
              \.\d* # mantissa of the form a.b or a.
          )?        # ? takes care of integers of the form a
         |\.\d+     # mantissa of the form .b
      )
      ([eE][+-]?\d+)?  # finally, optionally match an exponent
   $""")</code>

This pattern matches strings that represent floating-point numbers in either decimal or scientific notation. To extract the number from a string, simply call re_float.match(string).

For example:

<code class="python">m = re_float.match("4.5")
print(m.group(0))
# -> 4.5</code>

This code prints "4.5" to the console.

Extraction of Multiple Numbers from a String:

To extract multiple numbers from a larger string, the re.findall() function can be used with the same regex pattern:

<code class="python">s = """4.5 abc -4.5 abc - 4.5 abc + .1e10 abc . abc 1.01e-2 abc 
       1.01e-.2 abc 123 abc .123"""
print(re.findall(r"[+-]? *(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][+-]?\d+)?", s))
# -> ['4.5', '-4.5', '- 4.5', '+ .1e10', ' 1.01e-2',
#     '       1.01', '-.2', ' 123', ' .123']</code>

The above is the detailed content of How to Extract Double Values from Strings Using Regex?. For more information, please follow other related articles on the PHP Chinese website!