Re: Re: modified list interval calculation

• To: mathgroup at smc.vnet.net
• Subject: [mg21149] Re: [mg21058] Re: modified list interval calculation
• From: "Tomas Garza" <tgarza at mail.internet.com.mx>
• Date: Fri, 17 Dec 1999 01:21:58 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Deborah Leddon[Dleddon at students.cas.unt.edu] wrote:

> I am having trouble with the problem below:
>
> I am trying to remove from list, t, those numbers in list, nt, that
> match and then I want to calculate the differences (intervals )
> between succesive numbers in list, t, that do not contain the
> removed number. For example:
> the two lists are;
> t = {1,4,4.5,6,7,8,8.9,9,10,12,140,16,16.8,17,18,
> 	19,19.1,19.3,19.5,20}
> nt = {8,8.9,10,17}
>
> the resulting intervals would look like:
> 4 -1, 4.5 - 4, 6 - 4.5, 7 - 6, 140 -12, 16 - 140, 16.8 - 16, 19 - 18,
> 19.1 -19, 19.3 - 19.1, 19.5 - 19.3, 20 - 19.5
> and of course the final list would be:
> intervals = {3, .5, 1.5, 1, 128, -124, .8, 1, .1, .2, .2, .5};
>
> Note that 9 was omitted from the calculation of intervals because it
> would have been involved in a calculation with a removed number
> from the list, t.

Probably this could be improved, but anyway here it goes:

In[1]:=
t = {1, 4, 4.5, 6, 7, 8, 8.9, 9, 10, 12, 140, 16, 16.8, 17, 18,
19, 19.1, 19.3, 19.5, 20};
nt = {8, 8.9, 10, 17};

In[3]:=
ps = Position[t, x_ /; MemberQ[nt, x]]
Out[3]=
{{6}, {7}, {9}, {14}}
In[4]:=
c = ReplacePart[t, "*", ps]
Out[4]=
{1, 4, 4.5, 6, 7, "*", "*", 9, "*", 12, 140, 16, 16.8, "*", 18, 19, 19.1, \
19.3, 19.5, 20}
In[5]:=
cr = Rest[c]
Out[5]=
{4, 4.5, 6, 7, "*", "*", 9, "*", 12, 140, 16, 16.8, "*", 18, 19, 19.1, 19.3,
\
19.5, 20}
In[6]:=
br = Drop[c, -1]
Out[6]=
{1, 4, 4.5, 6, 7, "*", "*", 9, "*", 12, 140, 16, 16.8, "*", 18, 19, 19.1, \
19.3, 19.5}

The intervals you want are given by

In[7]:=
Cases[Transpose[{br, cr}], {x_?NumberQ, y_?NumberQ}]
Out[7]=
{{1, 4}, {4, 4.5}, {4.5, 6}, {6, 7}, {12, 140}, {140, 16}, {16, 16.8}, {18,
19}, {19, 19.1}, {19.1, 19.3}, {19.3, 19.5}, {19.5, 20}}

and the final list is

In[8]:=
intervals = % /. {x_, y_} -> y - x
Out[8]=
{3, 0.5, 1.5, 1, 128, -124, 0.8, 1, 0.1, 0.2, 0.2, 0.5}

Tomas Garza
Mexico City

```

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