Assignment 2: K-Means Clustering & Hierarchical Clustering

Question 1
Question 2

Question 1

We will first use the pasilla data from Bioconductor. You can load the gene-level read count matrix using the script below.

In this exercise we use K-Means clustering on randomly generated data using the kmeans() function.

set.seed(2)
#BiocManager::install("pasilla")
library (pasilla)

## Loading required package: DEXSeq

## Loading required package: BiocParallel

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##     table, tapply, union, unique, unsplit, which.max, which.min

## Welcome to Bioconductor
## 
##     Vignettes contain introductory material; view with
##     'browseVignettes()'. To cite Bioconductor, see
##     'citation("Biobase")', and for packages 'citation("pkgname")'.

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pasCts <- system.file ("extdata", "pasilla_gene_counts.tsv",
package ="pasilla", mustWork = TRUE )
cts <- as.matrix ( read.csv(pasCts, sep="\t", row.names="gene_id"))
t_cts <- t(cts)

What is the model organism being studied? How many genes and how many samples per condition were assayed

packageDescription("pasilla")

## Package: pasilla
## Title: Data package with per-exon and per-gene read counts of RNA-seq
##         samples of Pasilla knock-down by Brooks et al., Genome Research
##         2011.
## Version: 1.30.0
## Author: Wolfgang Huber, Alejandro Reyes
## Maintainer: Alejandro Reyes <alejandro.reyes.ds@gmail.com>
## Description: This package provides per-exon and per-gene read counts
##         computed for selected genes from RNA-seq data that were
##         presented in the article "Conservation of an RNA regulatory map
##         between Drosophila and mammals" by Brooks AN, Yang L, Duff MO,
##         Hansen KD, Park JW, Dudoit S, Brenner SE, Graveley BR, Genome
##         Res. 2011 Feb;21(2):193-202, Epub 2010 Oct 4, PMID: 20921232.
##         The experiment studied the effect of RNAi knockdown of Pasilla,
##         the Drosophila melanogaster ortholog of mammalian NOVA1 and
##         NOVA2, on the transcriptome.  The package vignette describes
##         how the data provided here were derived from the RNA-Seq read
##         sequence data that are provided by NCBI Gene Expression Omnibus
##         under accession numbers GSM461176 to GSM461181.
## biocViews: ExperimentData, Genome, Drosophila_melanogaster_Data,
##         RNASeqData
## License: LGPL
## Suggests: rmarkdown, BiocStyle, knitr, roxygen2
## Depends: R (>= 3.5.0), DEXSeq
## VignetteBuilder: knitr
## RoxygenNote: 7.2.3
## Encoding: UTF-8
## git_url: https://git.bioconductor.org/packages/pasilla
## git_branch: RELEASE_3_18
## git_last_commit: edbc4d8
## git_last_commit_date: 2023-10-24
## Date/Publication: 2023-10-26
## NeedsCompilation: no
## Packaged: 2023-10-26 15:29:26 UTC; biocbuild
## Built: R 4.3.2; ; 2024-02-10 21:58:07 UTC; windows
## 
## -- File: C:/Users/18327/AppData/Local/R/win-library/4.3/pasilla/Meta/package.rds

print(paste("The Model organism being studied is Drosophila_melanogaster from package info."))

## [1] "The Model organism being studied is Drosophila_melanogaster from package info."

print(paste("Number of genes:", nrow(cts)))

## [1] "Number of genes: 14599"

print(paste("Number of samples:", ncol(cts)))

## [1] "Number of samples: 7"

print(paste("Sample names are :", paste(colnames(cts), collapse=", ")))

## [1] "Sample names are : untreated1, untreated2, untreated3, untreated4, treated1, treated2, treated3"

print(paste("So there were three treated samples and four untreated samples that were assayed"))

## [1] "So there were three treated samples and four untreated samples that were assayed"

Compute the library size factor using the following three strategies, and generate a pairwise plot of the three sets of estimates.

##Method 1: Total Count
sample_tc <- matrix(rowSums(t_cts, na.rm = TRUE),nrow = nrow(t_cts))
tc_denom <- colSums(sample_tc)
n_sample_tc <- sample_tc/tc_denom

##Method 2: Median Ratio

col_sums <- colSums(t_cts, na.rm = TRUE)

# Create a vector to store Theta_j values
Theta_j <- numeric(length(col_sums))
l_cts<-log(t_cts)
l_cts[is.infinite(l_cts)] <- NA

# Apply condition to each column sum
for (i in seq_along(col_sums)) {
  if (col_sums[i] %in% c(0, 1)) {
    Theta_j[i] <- col_sums[i]
  } else {
    Theta_j[i] <- exp(mean(l_cts[, i], na.rm = TRUE))
  }
}

theta_jv <- Theta_j
# Reshape Theta_j into a matrix
Theta_j <- matrix(Theta_j, ncol = ncol(t_cts))

# Apply condition to each element
for (j in 1:14599) 
{
  for (i in 1:7)
{
    if (Theta_j[j] %in% c(0)) 
    {
       t_cts[i,j] <- t_cts[i,j] }
    else
    {
    t_cts[i,j] <- t_cts[i,j]/Theta_j[j] }
  }
}
sample_med  <- matrix(rowMedians(t_cts, na.rm = TRUE),nrow = nrow(t_cts))

## Method 3 using 75th Quantile
#sample_quantile <- apply(t_cts, 2, function(x) quantile(x, 0.75) / quantile(rowSums(t_cts), 0.75))
sample_quantile <-apply(t_cts, 1, function(x) quantile(x, 0.75))

# Combine results into a data frame
library_size_factors <- data.frame(
  Total_Count = sample_tc,
  Median_Ratio = sample_med,
  Quantile = sample_quantile
)
# Generate pairwise plot
#pairs(library_size_factors)
pairs(library_size_factors, main = "Pairs Plot of Library Size Factors")

Question 2

We will reuse the toy single-cell sequencing dataset of mouse liver from the Liver Cell Atlas (Guilliams et al., Cell 2022). The data has been subsetted, cleaned, and normalized. You will have the opportunity to learn these processes later on! For now, you can access the processed data from the “Data” tab under “Modules” in Canvas and use the readRDS function to read them.

You have previously carried out principal component analysis on this data. Now perform hierarchical clustering on the top 10 principal components, using complete linkage and Euclidean distance. Visualize your result. Bonus point: show colors on the dendrogram that correspond to the true underlying cell types.

      pbmc3=readRDS('C:/STAT646/mouse_liver_cts.RDS')
      tpbmc3 <- t(pbmc3)
      pbmc4=readRDS('C:/STAT646/mouse_liver_annot.RDS')
      library(irlba)

## Loading required package: Matrix

## 
## Attaching package: 'Matrix'

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      # prcomp_irlba
      pbmc3.pc2=prcomp_irlba(tpbmc3, n=10)
                      
      #install.packages("dendextend")
      suppressPackageStartupMessages(library(dendextend))
                      
      # Perform hierarchical clustering
      hc.complete <- hclust(dist(as.matrix(pbmc3.pc2$x), method = "euclidean"), method = "complete")
                      
      # Cut dendrogram into 4 clusters since we know 4 cell types
     clusters <- cutree(hc.complete, k = 4)
                      
      avg_dend_obj <- as.dendrogram(hc.complete)
      avg_col_dend <- color_branches(avg_dend_obj,col = pbmc4)
      plot(avg_col_dend, labels = NULL)
      legend("topright", legend = levels(pbmc4), col = unique(pbmc4), pch=16, title = "Cell Types")
      title('Hierarchical Clustering Dendogram for 10 PCAs', line = 3.4)

Apply K-means clustering to the top 10 principal components: use a correlation-based distance metric (Pearson correlation) and silhouette score to determine the optimal number of clusters. Visualize your results.

set.seed(2)
 # Perform kmeans clustering

x <- as.matrix(pbmc3.pc2$x)
dd <-as.matrix(as.dist(1 - cor(t(x))))
km.out <- kmeans(dd, 4,nstart = 20)
plot(dd, col = (km.out$cluster + 1), main = "K-Means Clustering Results with K=4", xlab = "", ylab = "", pch = 20, cex = 2)
legend("topleft", legend = unique(km.out$cluster), col = unique(km.out$cluster), pch = 20, cex = 1, title = "Clusters")

library(cluster)
silhouette_score <- function(k){
  km <- kmeans(x, centers = k, nstart=20)
  ss <- silhouette(km$cluster, dist(x))
  mean(ss[, 3])
}
k <- 2:10
avg_sil <- sapply(k, silhouette_score)
plot(k, type='b', avg_sil, xlab='Number of clusters', ylab='Average Silhouette Scores', frame=FALSE)
title("Average Silhouette Scores for Different Numbers of Clusters")

print(paste("Based on the plot for Silhouette Score, the optimum number of clusters would be 3"))

## [1] "Based on the plot for Silhouette Score, the optimum number of clusters would be 3"

With this chosen number of cluster and its corresponding cluster assignment, output the confusion matrix (predicted cluster IDs by true underlying cell types) and compute the adjusted rand index (ARI).

library(aricode)
km.outfinal <- kmeans(dd, 3,nstart = 20)
print(paste("Adjusted Rand Index (ARI) with 3 clusters for kmeans is"))

## [1] "Adjusted Rand Index (ARI) with 3 clusters for kmeans is"

ARI(km.outfinal$cluster, pbmc4)

## [1] 0.3875469

print(paste("Confusion Matrix is"))

## [1] "Confusion Matrix is"

cell_types <- pbmc4
kmclusters <- km.outfinal$cluster
table(kmclusters, cell_types)

##           cell_types
## kmclusters Endothelial cells Fibroblasts Hepatocytes Kupffer cells
##          1                 0           0        1488             0
##          2               424         412          18           154
##          3                 0           0        1306             0

Assignment 2: K-Means Clustering & Hierarchical Clustering

S. kotta, STAT 646

Question 1

Question 2