scipy.cluster.hierarchy.fcluster¶

scipy.cluster.hierarchy.
fcluster
(Z, t, criterion='inconsistent', depth=2, R=None, monocrit=None)[source]¶ Form flat clusters from the hierarchical clustering defined by the given linkage matrix.
Parameters:  Z : ndarray
The hierarchical clustering encoded with the matrix returned by the
linkage
function. t : scalar
 For criteria ‘inconsistent’, ‘distance’ or ‘monocrit’,
this is the threshold to apply when forming flat clusters.
 For ‘maxclust’ or ‘maxclust_monocrit’ criteria,
this would be max number of clusters requested.
 criterion : str, optional
The criterion to use in forming flat clusters. This can be any of the following values:
inconsistent
:If a cluster node and all its descendants have an inconsistent value less than or equal to t then all its leaf descendants belong to the same flat cluster. When no nonsingleton cluster meets this criterion, every node is assigned to its own cluster. (Default)
distance
:Forms flat clusters so that the original observations in each flat cluster have no greater a cophenetic distance than t.
maxclust
:Finds a minimum threshold
r
so that the cophenetic distance between any two original observations in the same flat cluster is no more thanr
and no more than t flat clusters are formed.monocrit
:Forms a flat cluster from a cluster node c with index i when
monocrit[j] <= t
.For example, to threshold on the maximum mean distance as computed in the inconsistency matrix R with a threshold of 0.8 do:
MR = maxRstat(Z, R, 3) cluster(Z, t=0.8, criterion='monocrit', monocrit=MR)
maxclust_monocrit
:Forms a flat cluster from a nonsingleton cluster node
c
whenmonocrit[i] <= r
for all cluster indicesi
below and includingc
.r
is minimized such that no more thant
flat clusters are formed. monocrit must be monotonic. For example, to minimize the threshold t on maximum inconsistency values so that no more than 3 flat clusters are formed, do:MI = maxinconsts(Z, R) cluster(Z, t=3, criterion='maxclust_monocrit', monocrit=MI)
 depth : int, optional
The maximum depth to perform the inconsistency calculation. It has no meaning for the other criteria. Default is 2.
 R : ndarray, optional
The inconsistency matrix to use for the ‘inconsistent’ criterion. This matrix is computed if not provided.
 monocrit : ndarray, optional
An array of length n1. monocrit[i] is the statistics upon which nonsingleton i is thresholded. The monocrit vector must be monotonic, i.e. given a node c with index i, for all node indices j corresponding to nodes below c,
monocrit[i] >= monocrit[j]
.
Returns:  fcluster : ndarray
An array of length
n
.T[i]
is the flat cluster number to which original observationi
belongs.
See also
linkage
 for information about hierarchical clustering methods work.
Examples
>>> from scipy.cluster.hierarchy import ward, fcluster >>> from scipy.spatial.distance import pdist
All cluster linkage methods  e.g.
scipy.cluster.hierarchy.ward
generate a linkage matrixZ
as their output:>>> X = [[0, 0], [0, 1], [1, 0], ... [0, 4], [0, 3], [1, 4], ... [4, 0], [3, 0], [4, 1], ... [4, 4], [3, 4], [4, 3]]
>>> Z = ward(pdist(X))
>>> Z array([[ 0. , 1. , 1. , 2. ], [ 3. , 4. , 1. , 2. ], [ 6. , 7. , 1. , 2. ], [ 9. , 10. , 1. , 2. ], [ 2. , 12. , 1.29099445, 3. ], [ 5. , 13. , 1.29099445, 3. ], [ 8. , 14. , 1.29099445, 3. ], [11. , 15. , 1.29099445, 3. ], [16. , 17. , 5.77350269, 6. ], [18. , 19. , 5.77350269, 6. ], [20. , 21. , 8.16496581, 12. ]])
This matrix represents a dendrogram, where the first and second elements are the two clusters merged at each step, the third element is the distance between these clusters, and the fourth element is the size of the new cluster  the number of original data points included.
scipy.cluster.hierarchy.fcluster
can be used to flatten the dendrogram, obtaining as a result an assignation of the original data points to single clusters.This assignation mostly depends on a distance threshold
t
 the maximum intercluster distance allowed:>>> fcluster(Z, t=0.9, criterion='distance') array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], dtype=int32)
>>> fcluster(Z, t=1.1, criterion='distance') array([1, 1, 2, 3, 3, 4, 5, 5, 6, 7, 7, 8], dtype=int32)
>>> fcluster(Z, t=3, criterion='distance') array([1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4], dtype=int32)
>>> fcluster(Z, t=9, criterion='distance') array([1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1], dtype=int32)
In the first case, the threshold
t
is too small to allow any two samples in the data to form a cluster, so 12 different clusters are returned.In the second case, the threshold is large enough to allow the first 4 points to be merged with their nearest neighbors. So here only 8 clusters are returned.
The third case, with a much higher threshold, allows for up to 8 data points to be connected  so 4 clusters are returned here.
Lastly, the threshold of the fourth case is large enough to allow for all data points to be merged together  so a single cluster is returned.