Re: Inverse of IntegerDigits? and "Index" function?

*To*: mathgroup at smc.vnet.net*Subject*: [mg3979] Re: Inverse of IntegerDigits? and "Index" function?*From*: rhall2 at umbc.edu (hall robert)*Date*: Mon, 13 May 1996 01:49:13 -0400*Organization*: University of Maryland, Baltimore County*Sender*: owner-wri-mathgroup at wolfram.com

In article <4menl1$jva at dragonfly.wolfram.com>, <pehowland at taz.dra.hmg.gb> wrote: >I'm playing around with some binary numbers, and am using IntegerDigits >to convert from a decimal integer to the binary notation. eg. > In[1]:= IntegerDigits[10,2] > Out[1]= {1,0,1,0} > >What is the function to convert back? eg. I want to do > In[2]:= DigitsToInteger[{1,0,1,0},2] >and get > Out[2]= 10 In[57]:= changeBaseToTen[base_, powers_List] := Apply[ Plus, powers Reverse[Map[base^#&, Range[Length[powers]] - 1]] ] In[49]:= a = IntegerDigits[10, 2] Out[49]= {1, 0, 1, 0} In[50]:= changeBaseToTen[2, a] Out[50]= 10 >Thus I want a function that works as follows: > > In[3]:= Map[Index[#]&, {2,6,3,9,10,2,4}] > Out[3]= {1,2,3,4,5,6,7} In[51]:= Range[Length[{2,6,3,9,10,2,4}]] Out[51]= {1, 2, 3, 4, 5, 6, 7} -- Bob Hall | "Know thyself? Absurd direction! rhall2 at gl.umbc.edu | Bubbles bear no introspection." -Khushhal Khan Khatak ==== [MESSAGE SEPARATOR] ====