Scanning a string for decimal numbers

Ruby
1

Hi all, how do you scan a string and avoid getting my decimal numbers
divided into 2 numbers.

Example:

a = “24,4 + 55,2”
a.scan! (/\d+/)
puts a

my output for a will be:
24
4
55
2

But I want to keep my decimal numbers intact like this:
24,4
55,2

How do I solve this problem without putting the numbers into seperate
strings?

2

“24,4 + 55,2”.scan /[\d,]+/

Kent

3

Kent S. wrote:

a = “24,4 + 55,2”
24,4
55,2

How do I solve this problem without putting the numbers into seperate
strings?

try
a.scan!(/\d+,\d+/)
Ernie

4

Jeppe J. wrote:

24
strings?
Hi Jeppe,
you can use the following:

a.scan /[-+]?[0-9]*,?[0-9]+/

which will take care of negative numbers as well.

HTH,
Antonio

5

a.scan /[-+]?[0-9]*,?[0-9]+/

Or to be less verbose you can use \d in place of [0-9] :slight_smile:

HTH
Antonio

6

On Feb 5, 2006, at 13:03, Antonio C. wrote:

a.scan /[-+]?[0-9]*,?[0-9]+/

Or to be less verbose you can use \d in place of [0-9] :slight_smile:

If you have Perl installed, the incantation

 perldoc -q float

gives some regexps for numbers.

– fxn

7

On Sun, 5 Feb 2006, Ernest Ellingson wrote:

But I want to keep my decimal numbers intact like this:
try
a.scan!(/\d+,\d+/)
Ernie

careful. you’ll kill negatives.

-a

8

Will that expression include both integers and decimal numbers?

9

Hi!

At Sun, 05 Feb 2006 11:43:52 +0000, Antonio C. wrote:

a.scan /[-+]?[0-9]*,?[0-9]+/

Shouldn’t that rather be the following?

a.scan /[-+]?([1-9]\d*(,[0-9]+)?)|(0(,[0-9]+)?)/

Josef ‘Jupp’ Schugt

10

Nice, that was the thing I was looking for :slight_smile:

2006/2/12, Wilson B. [email protected]:

11

On 2/4/06, Jeppe J. [email protected] wrote:

24
strings?

This should handle periods or commas as the separator.

a = “24,4 + 55,2 + 55 - 44,0”
=> “24,4 + 55,2 + 55 - 44,0”
a.scan /(\d+,?.?\d*)(?=\s|$)/
=> [[“24,4”], [“55,2”], [“55”], [“44,0”]]

12

This should handle periods or commas as the separator.

a = “24,4 + 55,2 + 55 - 44,0”
=> “24,4 + 55,2 + 55 - 44,0”
a.scan /(\d+,?.?\d*)(?=\s|$)/
=> [[“24,4”], [“55,2”], [“55”], [“44,0”]]

Some problems here:

  • signs are disregarded ("-24,4" becomes “24,4”)
  • Invalid numbers are accepted: eg. “24,.4” “24,.” “24.” “24,”
  • “.” should be escaped. As you used it here, it means “any character”
    (except newline), so many invalid numbers are accepted (e.g. “24w”…)
  • If something different from whitespace follows the number, it is not
    or false accepted, e.g. “24.4.” becomes “4.” instead of “24.4”
  • …

Alexis.

13

2006/2/12, Alexis R. [email protected]:

Some problems here:

Let me see if I got it right then. I’ll like to use periods only for my
decimal numbers. I also need normal integers so 24. being accepted won’t
matter. Will this fix the problems you presented?:
/[-+]?(\d+.?\d*)(?=\s|$)/

I don’t know if it takes care of the last problem, because I didn’t
understand it.

14

Seems I accidently got my text marked as a qoute in my last mail, so
I’ll
just send it a again:

Let me see if I got it right then. I’ll like to use periods only for my
decimal numbers. I also need normal integers so 24. being accepted won’t
matter. Will this fix the problems you presented?:
/[-+]?(\d+.?\d*)(?=\s|$)/

I don’t know if it takes care of the last problem, because I didn’t
understand it.

2006/2/12, Jeppe J. [email protected]:

15

Yes that worked, but I intend to convert the digits of my array to
floats,
and I get a NoMethodError on to_f now when I do this:

digits[0] = digits[0].to_f

I don’t understand that :-/

2006/2/12, Wilson B. [email protected]:

16

The scan process returns an array of arrays, so:
digits[0] is an Array containing ‘24.4’.
You could do:
digits.flatten!
just before digits[0], and get what you expect.

17

Well, that’s what I get for dashing off a quick e-mail before dinner.
The last problem Alexis mentioned is caused by the overly-specific
lookahead at the end. Here’s a version that fixes that:

irb(main):013:0> a = ‘24.5 + 24 + 24. + 24.4.’
=> “24.5 + 24 + 24. + 24.4.”
irb(main):014:0> a.scan /[-+]?(\d+(?:.\d+)?)(?=[^\d])/
=> [[“24.5”], [“24”], [“24”], [“24.4”]]
irb(main):015:0>

One of the characters ‘-’ or ‘+’, optionally
Followed by at least one digit.
Followed by an optional group containing a period, and one or more
digits.
The capturing group ends when the next character is something other
than a digit.

The (?:slight_smile: mess is there so that ‘24.’ doesn’t end up with the period on
the end.

18

ok, but I think but wouldn’t this regex do the same for me?:

/[-+]?\d+.?\d+/

Except that it will return an array containing my digit?

2006/2/12, Wilson B. [email protected]:

19

Yes, as long as the numbers are always at least two digits.

20

Hi!

At Sun, 12 Feb 2006 08:12:47 +0900, Jeppe J. wrote:

Will that expression include both integers and decimal numbers?

[-+]?([1-9]\d*(,[0-9]+)?)|(0(,[0-9]+)?)

has two parts:

[-+]?
([1-9]\d*(,[0-9]+)?)|(0(,[0-9]+)?)

The first one is an optional sign. The second one is an alternative
between to two cases:

[1-9]\d*(,[0-9]+)?
0(,[0-9]+)?

Let’s first consider the first case

[1-9]\d*(,[0-9]+)?

It has two parts, namely

[1-9]\d*
(,[0-9])?

The first part by itself covers all integers larger than zero. The
overall expression additionally covers all floating point numbers
larger than 1.

Now the second case

0(,[0-9]+)?

This one covers zero and all decimal numbers larger than 0 and smaller
than 1.

The regex I provided intentionally supports none of

[±],\d+
[±]0+\d+

You may as well use the shorter version

[-+]?(([1-9]\d*(,\d+)?)|(0(,\d+)?))

Wait a moment, I am not sure if that is correct. To be on the safe
side I’d rather use one of these where anything that follows the
optional sign has been put into another pair of parentheses:

[-+]?(([1-9]\d*(,[0-9]+)?)|(0(,[0-9]+)?))
[-+]?((([1-9]\d*(,\d+)?)|(0(,\d+)?)))

I am one of those guys who sometime run out of placeholders when doing
search and replace in vim (which has nine of them).

Josef ‘Jupp’ Schugt