How to manipulate cluster data point of Kmeans clustering algorithm
Using K-means clustering, as you said we specify the number of clusters but it's not actually possible to specify the percentage of data points. I would recommend using Fuzzy-C if you want to specify a exact percentage of data points  alloted for each cluster
In Kmeans clustering we can define number of cluster. But is it possible to define that cluster_1 will contain 20% data, cluster_2 will have 30% and cluster_3 will have rest of the data points?
I try to do it by python but couldn't.