converting long string to number

[Glen Rubin]

I am trying to convert a long string of numbers to a number, but get a
java.lang.numberformatexception

My long string of numbers has new line characters in it, so I am
filtering out the newline characters before converting it back to a
string. Then I try to use Integer. on it but get the above exception.

Code is as follows:
big-num-str is truncated for space's sake, is actually much much
longer!!

(def big-num-str "37107287533902102798797998220837590246510135740250
46376937677490009712648124896970078050417018260538
74324986199524741059474233309513058123726617309629
91942213363574161572522430563301811072406154908250
23067588207539346171171980310421047513778063246676
89261670696623633820136378418383684178734361726757
28112879812849979408065481931592621691275889832738
44274228917432520321923589422876796487670272189318
47451445736001306439091167216856844588711603153276
70386486105843025439939619828917593665686757934951....")

(Integer. (apply str (filter #(Character/isDigit %) big-num-str)))

[Chas Emerick]

Glen,

You want (java.math.BigInteger. "2342343..."). java.lang.Integer is
limited to 2^31-1.

- Chas

[Per Vognsen]

Though it might not be the best option here, the Clojure reader is
always ready to serve:

user> (type (read-string "123"))
java.lang.Integer
user> (type (read-string "123123123123123"))
java.lang.Long
user> (type (read-string "123123123123123123123123123123123123"))
java.math.BigInteger

Of course, it might also pose a bit of a security threat:

user> (read-string "#=(println \"I OWN YOU NOW!\")")
I OWN YOU NOW!
nil

:)

-Per

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[Richard Newman]

> Of course, it might also pose a bit of a security threat:
>
> user> (read-string "#=(println \"I OWN YOU NOW!\")")
> I OWN YOU NOW!
> nil
>
> :)

user=> (binding [*read-eval* false]
(read-string "#=(println \"I OWN YOU NOW!\")"))
java.lang.RuntimeException: java.lang.Exception: EvalReader not
allowed when *read-eval* is false. (NO_SOURCE_FILE:0)

[Mark Engelberg]

Another unadvertised function that is useful to be aware of is clojure.lang.Numbers/reduce which will simplify a number to its most simple type.  I often find that I want to use some BigInteger function, but then it is important to turn it back into a "typical Clojure number" at the end.

For example,

(defn next-prime [n] (clojure.lang.Numbers/reduce (.nextProbablePrime (BigInteger. (str n)))))

--Mark

[Per Vognsen]

In those hills yonder in the lands of Common Lisp, it's usually
considered good practice to blast the entire read table save for what
you need when you deal with untrusted data. Barring that, a better
option might be a more modular reader: read-number, read-symbol, etc.

-Per

[Richard Newman]

> In those hills yonder in the lands of Common Lisp, it's usually
> considered good practice to blast the entire read table save for what
> you need when you deal with untrusted data. Barring that, a better
> option might be a more modular reader: read-number, read-symbol, etc.

Clojure doesn't have a user-programmable reader, so much of the
readtable shenanigans we use in CL don't apply. But yes, specific
readers would be neat.

[Miki]

> You want (java.math.BigInteger. "2342343..."). java.lang.Integer is
> limited to 2^31-1.

Clojure has a "bigint" function, so (bigint (apply str (re-seq
#"[0-9]+" big-num-str))) will work as well.

[feka]

Looks like you are doing the 13th Project Euler problem. That means
you have exactly one hundred 50 digit numbers. I am new to Clojure but
AFAIK you wont be able to handle a 5000 digit number in it. You have
to find another way. There is at least one... ;-)

--Feka

[feka]

Really embarrassing in two ways:
- Could not remove my previous post. :-)
- I should have tried to create such a big number (at least after
reading all the answers here) before posting... It is possible to
crate a 50000 digit big integer.

PS: Watch out though. The aim of the problem is to add up those 50-
digit numbers and not to create one 50000-digit number.

--feka