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Re: FromDigits[{135,21}] -> 1371 (??!!)

• To: mathgroup at smc.vnet.net
• Subject: [mg53740] Re: [mg53725] FromDigits[{135,21}] -> 1371 (??!!)
• From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
• Date: Wed, 26 Jan 2005 04:36:14 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Zak, 
please see below:

>-----Original Message-----
>From: Zak Seidov [mailto:seidovzf at yahoo.com] 
To: mathgroup at smc.vnet.net
>Sent: Tuesday, January 25, 2005 11:03 AM
>To: mathgroup at smc.vnet.net
>Subject: [mg53740] [mg53725] FromDigits[{135,21}] -> 1371 (??!!)
>
>Can anyone please explain what happens,
>if "Digits" actually are "integers":
>FromDigits[{3,2}]
>32(!)
>FromDigits[{13,2}]
>132 (!!)
>FromDigits[{135,2}],
>1352 (!!!)
>FromDigits[{1355078,9}]
>13550789 (!!!!!!!)
>it's OK above,
>but:
>FromDigits[{135,21}]
>1371 (??!!)
>FromDigits[{13,23}]
>153 (??!!)
>FromDigits[{3,23}]
>53 (??!!)
>

The answer is simple, if we ask how FromDigits should work, i.e. let's
implement (part of) it:

In[2]:=
fromdigits[l : {__Integer?NonNegative}, base : (_Integer?Positive) : 10]
:=
  Fold[#2 + #1*base &, 0, l]

This is how it works.


In[3]:= fromdigits[{3, 2}]
Out[3]= 32
In[4]:= fromdigits[{13, 2}]
Out[4]= 132
In[5]:= fromdigits[{135, 2}]
Out[5]= 1352
In[6]:= fromdigits[{1355078, 9}]
Out[6]= 13550789
In[7]:= fromdigits[{135, 21}]
Out[7]= 1371
In[8]:= fromdigits[{13, 23}]
Out[8]= 153
In[9]:= fromdigits[{3, 23}]
Out[9]= 53



>And how to get integer 1323 from  list {13,23}?
>

e.g. 

In[10]:= fromdigits[{13, 23}, 100]
Out[10]= 1323

In[11]:= FromDigits[{13, 23}, 100]
Out[11]= 1323

This might not be usable for your application, if not

>So, or there is a better way:
>li={135,42};FromDigits[Flatten[{IntegerDigits[li[[1]]],IntegerD
>igits[li[[2]]]}]]->
>13542
>

this or something equivalent

In[12]:= FromDigits[Join @@ IntegerDigits /@ {13, 23}]
Out[12]= 1323


>Many thanks,
>and if you please send copy to
>seidovzf at yahoo.com
>Zak
>
>PS I use M4.
>M5 also gives
>FromDigits[{135,21}]
>1371 (??!!)
>
>

Of course, it should!

--
Hartmut Wolf