Re: Replacing elements in a list

• To: mathgroup at smc.vnet.net
• Subject: [mg90105] Re: [mg90092] Replacing elements in a list
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sun, 29 Jun 2008 05:34:55 -0400 (EDT)

```pairs = {{1, 2}, {3, 4}, {1, {1, 2}}};

elem = Union[Flatten[pairs, 1]]

{1,2,3,4,{1,2}}

pairs /. {x_, y_List} :>
{x, Position[elem, y][[1, 1]]}

{{1, 2}, {3, 4}, {1, 5}}

Bob Hanlon

---- yedidel at gmail.com wrote:
> Hello,
>
> I have a list of pairs that looks like this:
>
> {{1,2},{3,4},{1,{1,2}}}
>
> Each pair element can be a pair by itself.
>
> I have another list which lists all elements possible:
> {1,2,3,4,{1,2}}
>
> Now I want to create a list of rules that will take the element list
> and give it a running number ({1,2} will be 5 in this example)
>
> after that I want to apply those rules to the pair list BUT that will
> do it only from the second level down. This means that the final
> result should be:
>
> {{1,2},{3,4},{1,5}}
> without the first pair {1,2} changing to 5 because it is a pair and
> not an element.
>
>

```

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