# [scikit-learn] What is the FeatureAgglomeration algorithm?

Gael Varoquaux gael.varoquaux at normalesup.org
Thu Jul 26 01:38:54 EDT 2018

```No.

⁣Sent from my phone. Please forgive typos and briefness.​

On Jul 26, 2018, 07:28, at 07:28, Raphael C <drraph at gmail.com> wrote:
>Is it expected that all three linkages options should give the same
>result
>in my toy example?
>
>Raphael
>
>On Thu, 26 Jul 2018 at 06:20 Gael Varoquaux
><gael.varoquaux at normalesup.org>
>wrote:
>
>> FeatureAgglomeration uses the Ward, complete linkage, or average
>> algorithms, depending on the choice of "linkage". These are well
>> documented in the literature, or on wikipedia.
>>
>> Gaël
>>
>> On Thu, Jul 26, 2018 at 06:05:21AM +0100, Raphael C wrote:
>> > Hi,
>>
>> > I am trying to work out what, in precise mathematical terms,
>> > [FeatureAgglomeration][1] does and would love some help. Here is
>some
>> example
>> > code:
>>
>>
>> >     import numpy as np
>> >     from sklearn.cluster import FeatureAgglomeration
>> >     for S in ['ward', 'average', 'complete']:
>> >         FA = FeatureAgglomeration(linkage=S)
>> >         print(FA.fit_transform(np.array([[-50,6,6,7,],
>[0,1,2,3]])))
>>
>> > This outputs:
>>
>> >
>>
>> >     [[  6.33333333 -50.        ]
>> >      [  2.           0.        ]]
>> >     [[  6.33333333 -50.        ]
>> >      [  2.           0.        ]]
>> >     [[  6.33333333 -50.        ]
>> >      [  2.           0.        ]]
>>
>> > Is it possible to say mathematically how these values have been
>computed?
>>
>> > Also, what exactly does linkage do and why doesn't it seem to make
>any
>> > difference which option you choose?
>>
>> > Raphael
>>
>>
>> >   [1]: http://scikit-learn.org/stable/modules/generated/
>> > sklearn.cluster.FeatureAgglomeration.html
>>
>> > PS I also asked at
>> > https://stackoverflow.com/questions/51526616/
>> >
>>
>>
>>
>> > _______________________________________________
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>> > scikit-learn at python.org
>> > https://mail.python.org/mailman/listinfo/scikit-learn
>>
>>
>> --
>>     Gael Varoquaux
>>     Senior Researcher, INRIA Parietal
>>     NeuroSpin/CEA Saclay , Bat 145, 91191 Gif-sur-Yvette France
>>     Phone:  ++ 33-1-69-08-79-68
>>     http://gael-varoquaux.info
>> _______________________________________________
>> scikit-learn mailing list
>> scikit-learn at python.org
>> https://mail.python.org/mailman/listinfo/scikit-learn
>>
>
>
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