how to interpret a hierarchical clustering in the heatmap in the picture bellow? I am trying to interpret the heatmap which was created based on a agglomerative hierarchical clustering. I am not sure what exactly the heatmap does, having in mind that I see on left hand side clustering done on symptoms and on the top of the heatmap I get a clustering of the bellow labels.
Can someone please help? Here is the picture
Also, this is the code I have used to generate the heatmap:
library(pheatmap)
pheatmap(t(dt_wd[-1]), cluster_rows = TRUE, cluster_cols = TRUE, clustering_distance_cols = &quot;euclidean&quot;,
         clustering_distance_rows = &quot;euclidean&quot;, clustering_method = &quot;ward&quot;,  cutree_cols = 4, 
         main = &quot;Cluster of comorbidities based on Covid-19 Symptoms&quot;)
This type of plot is refereed as Double Dendogram or Coloured Heatmap.
As seen in the code you have used Single Linkage Method for clustering.It yields clusters in which individuals are added sequentially to a single group.
From the example we can see that label dia2,ht and ob belong to one group but ht and ob are more correlated with each other.

I am not sure what exactly the heatmap does

The color of a cell is proportional to its position along a color gradient.
Heatmap is helpful in finding the correlation coefficient. It can helps us to visualize the difference in value within clusters. It's more like a color representation of value.