Importing a number after a string?

Questions
1

Hi,

How to copy a real number after a string in a text file. This number can be in any form (integer /decimal /exponential). For example

aaaa bbb (xyz / cc.dd ee) : = 3.456e2

or

aaaa bbb (xyz / cc.dd ee) : = 345.6

or

aaaa bbb (xyz / cc.dd ee) : = 345

I need a function, which can copy the numerical value after “aaaa bbb (xyz / cc.dd ee) : =” irrespective of its form.

Thanks for the help.

2

This thread should help. That post has some suggestions for simple formatting. To get really good formatting, I have a “one line” external function that calls the C function, sprintf. I can repost it here if you are interested.

Regards

3

How about

extract[s_] := 
 s // StringSplit[#, "aaaa bbb (xyz / cc.dd ee) : = "] & // First // 
  Read[StringToStream[#], Number] &

s1 = "aaaa bbb (xyz / cc.dd ee) : = 3.456e2"
s2 = "aaaa bbb (xyz / cc.dd ee) : = 345.6"
s3 = "aaaa bbb (xyz / cc.dd ee) : = 345"

extract /@ {s1, s2, s3}
(* {345.6, 345.6, 345} *)
4

Appreciate your help. I went through the post and the other one mentioned there. Not understood all the steps yet, but my problem is more of copying a numerical value after a string in the text file, rather than changing its accuracy or format. I am bit confused now, whether I need to convert the string to CForm for Mathematica to read it in the text file. However, my previous experience is that Mathematica can read a string in a text file, as it is. Please correct me if I am wrong.

In my case, it would be fine if I am able to copy a number in its given form, as long as it is of correct numerical value for all possible formats. For example, if the number is 1.23e2 in the text file, I am not worried whether I get the output as 1.23e2 or 123 or 123.00 or 1.23*10^2 etc.

Hope it explains my problem little better. Thanks once again.

5

Hope it explains my problem little better

Not really. 1.23e2 is not a valid format for a number in WL. 1.23*^2 or 1.23*10^2 are valid. The code I provided converts the invalid form to the valid one and the result is a number, not a string.

If you want a string result then just split the string

StringSplit[#, "aaaa bbb (xyz / cc.dd ee) : = "] & /* First /@ {s1, s2, s3}
(* {"3.456e2", "345.6", "345"} *)
6

Basically the same as Rohits last post, but without need to specify the leading part of the source strings:

s1 = "aaaa bbb (xyz / cc.dd ee) : = 3.456e2";
s2 = "pqr : = 345.6";
s3 = "stu / (v w x) : = 345";

Last /@ StringSplit[{s1, s2, s3}]
(* {"3.456e2","345.6","345"} *)
7

Thanks. It worked for any kind of numerical value. However, if the i/p has more than one strings present, this method does not work. For example if

s4="pqr : = 3
 aaaa bbb (xyz / cc.dd ee) : = 3456e2";
extract /@ s4

error message is -

Read::readn: Invalid real number found when reading from StringToStream[pqr : = 5].

This point is important as I have to use this method to extract a parameter from a text file having large number of strings, each followed by a number.

Thanks for your help once again..

8

Well, now you have changed the requirements. It would have been better if your original question stated the requirements clearly and completely.

In the s4 example there is a newline \n character separating the two cases. Is that always true or can s4 be like this?

s4 = "pqr : = 3 aaaa bbb (xyz / cc.dd ee) : = 3456e2";

or

s4 = "pqr : = 3aaaa bbb (xyz / cc.dd ee) : = 3456e2";

Is the number always preceded by : = or are there other possible character sequences?

If there is always a newline and always preceded by : = then

(s4 // StringSplit[#, " : = " | "\n"] &)[[2 ;; ;; 2]]
(* {"3", "3456e2"} *)

That will extract the numbers as strings, you can convert to numeric by mapping

Read[StringToStream[#], Number] & /@ {"3", "3456e2"}
(* {3, 345600} *)

s5 = "pqr : = 3
 aaaa bbb (xyz / cc.dd ee) : = 3456e2
abc : = 345.6";

(s5 // StringSplit[#, " : = " | "\n"] &)[[2 ;; ;; 2]]
(* {"3", "3456e2", "345.6"} *)
9

Well, now you have changed the requirements. It would have been better if your original question stated the requirements clearly and completely.

Actually, I mentioned that I need to copy a number from the text file, after a particular string. Anyways, finally, StringSplit worked, however I had to make some changes to what you suggested. Thanks for the help.