Re: Cases and Nonatomic expression

• To: mathgroup at smc.vnet.net
• Subject: [mg56722] Re: Cases and Nonatomic expression
• From: Curt Fischer <tentrillion at gmail.NOSPAM.com>
• Date: Thu, 5 May 2005 06:01:07 -0400 (EDT)
• References: <d59lfg\$6i6\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Swati Shah wrote:
> Hi Everyone
>
> I have a list
> k = {{1,1,2,2,3}, {1,2,2,2,3}, {2,3,3,3,3}, {5,2,2,2,1}, {6,1,1,1,1},
> {6,1,1,1,1}}
>
> If the first element of the sublist is 1 I want to append the sublist to
> g1, if it starts with 2 then append g2 or starts with 6 then append to g6
>
> I used cases and did the following:
> m1 = Cases[k, {1, __}];
> m2 = Cases[k, {2, __}];
> m3 = Cases[k, {3, __}];
> m4 = Cases[k, {4, __}];
> m5 = Cases[k, {5, __}];
> m6 = Cases[k, {6, __}];
>
> However, instead of typing each one of these lines separately, it
> would be nice to use just a simple Map or something or a for loop (as
> I have more than 50 different start values)

[...]

> However outside the for loop the values of g1..g6 is empty.
>
> b) I tried using MAP (in the similar way as the for)
>
> But I get the following error:
> Append::normal: Nonatomic expression expected at position 1 in Append[g1,{1, \
> 168, 0.695873, 6.54462, 62.4578, 82.5056}]
In[1]:=
k = {{1, 1, 2, 2, 3},
{1, 2, 2, 2, 3},
{2, 3, 3, 3, 3},
{5, 2, 2, 2, 1},
{6, 1, 1, 1, 1},
{6, 1, 1, 1, 1}};

You can Map[] Cases[] onto your domain of interest, which in the test
problem was {1,2,3,4,5,6}, by using the command below.  This creates a
vector m whose elements are things that will later be appended to the
corresponding elements of g.

In[2]:=
m = (Cases[k, {#1, ___}] & ) /@ Range[1, 6]

Out[2]={{{1, 1, 2, 2, 3},    {1, 2, 2, 2, 3}},   {{2, 3, 3, 3, 3}}, {},
{},   {{5, 2, 2, 2, 1}},   {{6, 1, 1, 1, 1},    {6, 1, 1, 1, 1}}}

I made up an initialization for your list g.  You could use empty lists
too if you wanted.

In[3]:=
g = {{foo1}, {foo2}, {foo3},
{foo4}, {foo5}, {foo6}};

Then, I mapped the pure function AppendTo[g[[#]],m[[#]]] onto the domain
of this problem to form the updated g.

In[4]:=
(AppendTo[g[[#1]],
m[[#1]]] & ) /@
Range[1, 6];
In[5]:=
ColumnForm[g]

Out[5]=
{foo1, {{1, 1, 2, 2, 3}, {1, 2, 2, 2, 3}}}
{foo2, {{2, 3, 3, 3, 3}}}
{foo3, {}}
{foo4, {}}
{foo5, {{5, 2, 2, 2, 1}}}
{foo6, {{6, 1, 1, 1, 1}, {6, 1, 1, 1, 1}}}

Is this what you wanted?

--
Curt Fischer

```

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