R语言层次聚类问题：手动距离矩阵构建单连接树状图报错

Hey there! Let's walk through solving this error step by step. First, let's make sure your distance matrix is properly defined and formatted for R's clustering functions.

Step 1: Correctly Define Your Distance Matrix #

First, let's finish writing out your matrix code properly (you had a trailing ...):

# Define the 11x11 distance matrix
mat <- matrix(c(0,1,2,3,3,1,2,2,2,3,2,
                1,0,1,2,2,2,1,2,3,2,3,
                2,1,0,1,1,2,2,1,2,3,3,
                3,2,1,0,1,3,3,2,3,4,4,
                3,2,1,1,0,3,3,2,3,4,4,
                1,2,2,3,3,0,1,1,1,2,1,
                2,1,2,3,3,1,0,1,2,1,2,
                2,2,1,2,2,1,1,0,1,2,2,
                2,3,2,3,3,1,2,1,0,1,1,
                3,2,3,4,4,2,1,2,1,0,1,
                2,3,3,4,4,1,2,2,1,1,0), 
              nrow=11, byrow=TRUE)

Step 2: Verify the Distance Matrix is Valid #

Distance matrices must satisfy two key rules for clustering:

1. Symmetric: mat[i,j] must equal mat[j,i] for all i,j
2. Diagonal values are 0: All elements on the main diagonal are 0 (your matrix already has this)

Check symmetry with this quick test:

all(mat == t(mat)) # Should return TRUE

If this returns FALSE, you have a typo in your manual matrix entry—double-check the values to fix mismatched pairs.

Step 3: Convert to a dist Object #

R's hclust() function works best with a dist class object (a compressed representation of the distance matrix) instead of the full 11x11 matrix. Convert it like this:

dist_mat <- as.dist(mat)

Step 4: Build the Single Linkage Dendrogram #

Now run the single linkage clustering and plot the dendrogram:

# Perform single linkage clustering
hc_single <- hclust(dist_mat, method = "single")

# Plot the dendrogram
plot(hc_single, main = "Single Linkage Dendrogram (11 Vertices)")

Common Causes of Your Error #

• Not using a dist object: Passing the full 11x11 matrix directly to hclust() can cause parsing issues, even if the matrix is valid. Converting to dist resolves this.
• Asymmetric matrix: If your manual entry had a typo (e.g., mat[1,6] = 1 but mat[6,1] = 2), this breaks the distance matrix rules and triggers errors. Use the symmetry check above to catch this.

Running these steps should give you a working single linkage dendrogram without errors!

内容的提问来源于stack exchange，提问作者user2095405