def drawDendrogram(cluster, file="dendrogram.jpg"):
"""
Given a cluster, outputs a dendrogram depiction of that cluster as
a jpg image. The lengths of the lines depicting a pair of
children are proportional to the degree of dissimilarity between
the pair.
"""
imageHeight = getWidth(cluster) * 20
imageWidth = 1200
clusterDepth = getDepth(cluster)
scaling = float(imageWidth-150)/clusterDepth
# Create a new image with a white background
img = Image.new('RGB',(imageWidth,imageHeight), (255,255,255))
draw = ImageDraw.Draw(img)
# Draw the dendrogram
draw.line((0,imageHeight/2,10,imageHeight/2), fill=(0,0,0))
drawNode(draw, cluster, 10, imageHeight/2, scaling)
# Save the image
img.save(file,'JPEG')
def drawNode(draw, cluster, x, y, scaling):
"""
Given a DrawImage 'draw', and cluster 'cluster', draw the
dendrogram representing the cluster with its root located at x,y.
"""
if cluster.left == None and cluster.right == None:
# Draw a leaf node (i.e. just print the label)
draw.text((x+5,y-7),cluster.name,(0,0,0))
else:
# Draw a branch node
h1 = getWidth(cluster.left) * 20
h2 = getWidth(cluster.right) * 20
branchLength = cluster.error * scaling
y0 = y - h2/2
y1 = y + h1/2
draw.line((x,y0,x,y1), fill=(0,0,0))
draw.line((x,y0,x+branchLength,y0), fill=(0,0,0))
draw.line((x,y1,x+branchLength,y1), fill=(0,0,0))
drawNode(draw, cluster.left, x+branchLength, y0, scaling)
drawNode(draw, cluster.right, x+branchLength, y1, scaling)
