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RE: Replacement Rule


Brian,

A more efficient solution to your problem would be

l1 = {{1, 2}, {3, 4}, {5, 6}};
l2 = {{3, 4}, {5, 6}};

First /@ l1
{1, 3, 5}

First /@ l2
{3, 5}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 


> From: Brian Higgins [mailto:bghiggins at ucdavis.edu]
To: mathgroup at smc.vnet.net
> 
> I have the following list
> 
> l1={{1,2},{3,4},{5,6}};
> 
> and then I operate on it with the following pattern/replacement rule
> 
> In[3]:= l1 /. {x_, y_} -> x
> 
> Out[3]= {1, 3, 5}
> 
> This is what I would expect. Now consider the following list
> 
> In[4]:= l2 = {{3, 4}, {5, 6}};
> 
> Then I use the same pattern/replacement rule 
> 
> In[5]:=l2 /. {x_, y_} -> x
> 
> Out[5]= {3, 4}
> 
> I was hoping to get
> 
> {3,5}
> 
> What am I missing? The FullForm of l2 is basically the same structure
> as l1, as far as I can tell....
> 
> Brian
> 


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