正确使用 Mathematica Gather/Collect [英] Using Mathematica Gather/Collect properly

问题描述

我如何使用 Mathematica 的 Gather/Collect/Transpose 函数进行转换:

How do I use Mathematica's Gather/Collect/Transpose functions to convert:

{ { {1, foo1}, {2, foo2}, {3, foo3} }, { {1, bar1}, {2, bar2}, {3, bar3} } } 

到

{ {1, foo1, bar1}, {2, foo2, bar2}, {3, foo3, bar3} } 

谢谢！我希望有一个简单的方法，但我想不是！

Thanks! I was hoping there was a simple way, but I guess not!

推荐答案

这是您的列表:

tst = {{{1, foo1}, {2, foo2}, {3, foo3}}, {{1, bar1}, {2, bar2}, {3,  bar3}}}

这是一种方法:

In[84]:= 
Flatten/@Transpose[{#[[All,1,1]],#[[All,All,2]]}]&@
  GatherBy[Flatten[tst,1],First]

Out[84]= {{1,foo1,bar1},{2,foo2,bar2},{3,foo3,bar3}}

编辑

这是一个完全不同的版本，只是为了好玩:

Here is a completely different version, just for fun:

In[106]:= 
With[{flat = Flatten[tst,1]},
   With[{rules = Dispatch[Rule@@@flat]},
       Map[{#}~Join~ReplaceList[#,rules]&,DeleteDuplicates[flat[[All,1]]]]]]

Out[106]= {{1,foo1,bar1},{2,foo2,bar2},{3,foo3,bar3}}

编辑 2

这是另一种方式，使用链表和内部函数来累积结果:

And here is yet another way, using linked lists and inner function to accumulate the results:

In[113]:= 
Module[{f},f[x_]:={x};
  Apply[(f[#1] = {f[#1],#2})&,tst,{2}];
  Flatten/@Most[DownValues[f]][[All,2]]]

Out[113]= {{1,foo1,bar1},{2,foo2,bar2},{3,foo3,bar3}}

编辑 3

好的，对于那些认为以上所有内容都过于复杂的人，这里有一个非常简单的基于规则的解决方案:

Ok, for those who consider all of the above too complicated, here is a really simple rule - based solution:

In[149]:= 
GatherBy[Flatten[tst, 1], First] /. els : {{n_, _} ..} :> {n}~Join~els[[All, 2]]

Out[149]= {{1, foo1, bar1}, {2, foo2, bar2}, {3, foo3, bar3}}

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