Hierarchical clustering is a method of cluster analysis that creates a hierarchical representation of the clusters in a dataset. The method starts by treating each data point as a separate cluster and then iteratively combines the closest clusters until a stopping criterion is reached. A dendrogram is a tree-structured graph used to illustrate the hierarchical relationships among the clusters. The result of a clustering is presented either as the distance or the similarity between the clustered rows or columns depending on the selected distance measure.