How to reorder cluster leaves (columns) when plotting pheatmap in R?

Question

I am plotting a set of 15 samples clustered in three groups A, B, C, and the heatmap orders them such as C, A, B. (I have read this is due to that it plots on the right the cluster with the strongest similarity). I would like to order the clusters so the leaves of the cluster are seen as A, B, C (therefore reorganising the order of the cluster branches. Is there a function that can help me do this?

The code I have used:

library(pheatmap)

pheatmap(mat, annotation_col = anno, 
    color = colorRampPalette(c("blue", "white", "red"))(50), show_rownames = F)

(cluster_cols=FALSE would not cluster the samples at all, but that is not what I want)

I have also found on another forum this, but I am unsure how to change the function code and if it would work for me:

clustering_callback callback function to modify the clustering. Is called with two parameters: original hclust object and the matrix used for clustering. Must return a hclust object.

Answer 1

In this case, luckily clustering of the columns coincides with sample number order, (which is similar to dendrogram) so I added cluster_cols = FALSE and solved the issue of re-clustering the columns (and avoided writing the callback function.

pheatmap(mat, 
         annotation_col = anno, 
         fontsize_row = 2, 
         show_rownames = T, 
         cutree_rows = 3, 
         cluster_cols = FALSE)