Article Outline
Python matplotlib example 'PythonClusteringApp'
Functions in program:
def plot(Xs, predictions):def evaluate_learners(X):def reduce_dimensions(X):def get_features(frame):def download_data():
Modules used in program:
import matplotlib.pyplot as pltimport numpy as np
python PythonClusteringApp
Python matplotlib example: PythonClusteringApp
'''
This script perfoms the basic process for applying a machine learning
algorithm to a dataset using Python libraries.
The four steps are:
1. Download a dataset (using pandas)
2. Process the numeric data (using numpy)
3. Train and evaluate learners (using scikit-learn)
4. Plot and compare results (using matplotlib)
The data is downloaded from URL, which is defined below. As is normal
for machine learning problems, the nature of the source data affects
the entire solution. When you change URL to refer to your own data, you
will need to review the data processing steps to ensure they remain
correct.
============
Example Data
============
The example is from http://archive.ics.uci.edu/ml/datasets/Water+Treatment+Plant
It contains a range of continuous values from sensors at a water
treatment plant, and the aim is to use unsupervised learners to
determine whether the plant is operating correctly. See the linked page
for more information about the data set.
This script uses unsupervised clustering learners and dimensionality
reduction models to find similar values, outliers, and visualize the
classes.
'''
# Remember to update the script for the new data when you change this URL
URL = "http://archive.ics.uci.edu/ml/machine-learning-databases/water-treatment/water-treatment.data"
# Uncomment this call when using matplotlib to generate images
# rather than displaying interactive UI.
#import matplotlib
#matplotlib.use('Agg')
from pandas import read_table
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.ticker import MaxNLocator
try:
# [OPTIONAL] Seaborn makes plots nicer
import seaborn
except ImportError:
pass
# =====================================================================
def download_data():
'''
Downloads the data for this script into a pandas DataFrame.
'''
# If your data is in an Excel file, install 'xlrd' and use
# pandas.read_excel instead of read_table
#from pandas import read_excel
#frame = read_excel(URL)
# If your data is in a private Azure blob, install 'azure' and use
# BlobService.get_blob_to_path() with read_table() or read_excel()
#import azure.storage
#service = azure.storage.BlobService(ACCOUNT_NAME, ACCOUNT_KEY)
#service.get_blob_to_path(container_name, blob_name, 'my_data.csv')
#frame = read_table('my_data.csv', ...
frame = read_table(
URL,
# Uncomment if the file needs to be decompressed
#compression='gzip',
#compression='bz2',
# Specify the file encoding
# Latin-1 is common for data from US sources
encoding='latin-1',
#encoding='utf-8', # UTF-8 is also common
# Specify the separator in the data
sep=',', # comma separated values
#sep='\t', # tab separated values
#sep=' ', # space separated values
# Ignore spaces after the separator
skipinitialspace=True,
# Treat question marks as missing values
na_values=['?'],
# Generate row labels from each row number
index_col=None,
#index_col=0, # use the first column as row labels
#index_col=-1, # use the last column as row labels
# Generate column headers row from each column number
header=None,
#header=0, # use the first line as headers
# Use manual headers and skip the first row in the file
#header=0,
#names=['col1', 'col2', ...],
)
# Return a subset of the columns
#return frame[['col1', 'col4', ...]]
# Return the entire frame
#return frame
# Return all except the first column
del frame[frame.columns[0]]
return frame
# =====================================================================
def get_features(frame):
'''
Transforms and scales the input data and returns a numpy array that
is suitable for use with scikit-learn.
Note that in unsupervised learning there are no labels.
'''
# Replace missing values with 0.0
# or we can use scikit-learn to calculate missing values below
#frame[frame.isnull()] = 0.0
# Convert values to floats
arr = np.array(frame, dtype=np.float)
# Impute missing values from the mean of their entire column
from sklearn.preprocessing import Imputer
imputer = Imputer(strategy='mean')
arr = imputer.fit_transform(arr)
# Normalize the entire data set to mean=0.0 and variance=1.0
from sklearn.preprocessing import scale
arr = scale(arr)
return arr
# =====================================================================
def reduce_dimensions(X):
'''
Reduce the dimensionality of X with different reducers.
Return a sequence of tuples containing:
(title, x coordinates, y coordinates)
for each reducer.
'''
# Principal Component Analysis (PCA) is a linear reduction model
# that identifies the components of the data with the largest
# variance.
from sklearn.decomposition import PCA
reducer = PCA(n_components=2)
X_r = reducer.fit_transform(X)
yield 'PCA', X_r[:, 0], X_r[:, 1]
# Independent Component Analysis (ICA) decomposes a signal by
# identifying the independent contributing sources.
from sklearn.decomposition import FastICA
reducer = FastICA(n_components=2)
X_r = reducer.fit_transform(X)
yield 'ICA', X_r[:, 0], X_r[:, 1]
# t-distributed Stochastic Neighbor Embedding (t-SNE) is a
# non-linear reduction model. It operates best on data with a low
# number of attributes (<50) and is often preceded by a linear
# reduction model such as PCA.
from sklearn.manifold import TSNE
reducer = TSNE(n_components=2)
X_r = reducer.fit_transform(X)
yield 't-SNE', X_r[:, 0], X_r[:, 1]
def evaluate_learners(X):
'''
Run multiple times with different learners to get an idea of the
relative performance of each configuration.
Returns a sequence of tuples containing:
(title, predicted classes)
for each learner.
'''
from sklearn.cluster import (MeanShift, MiniBatchKMeans,
SpectralClustering, AgglomerativeClustering)
learner = MeanShift(
# Let the learner use its own heuristic for determining the
# number of clusters to create
bandwidth=None
)
y = learner.fit_predict(X)
yield 'Mean Shift clusters', y
learner = MiniBatchKMeans(n_clusters=2)
y = learner.fit_predict(X)
yield 'K Means clusters', y
learner = SpectralClustering(n_clusters=2)
y = learner.fit_predict(X)
yield 'Spectral clusters', y
learner = AgglomerativeClustering(n_clusters=2)
y = learner.fit_predict(X)
yield 'Agglomerative clusters (N=2)', y
learner = AgglomerativeClustering(n_clusters=5)
y = learner.fit_predict(X)
yield 'Agglomerative clusters (N=5)', y
# =====================================================================
def plot(Xs, predictions):
'''
Create a plot comparing multiple learners.
`Xs` is a list of tuples containing:
(title, x coord, y coord)
`predictions` is a list of tuples containing
(title, predicted classes)
All the elements will be plotted against each other in a
two-dimensional grid.
'''
# We will use subplots to display the results in a grid
nrows = len(Xs)
ncols = len(predictions)
fig = plt.figure(figsize=(16, 8))
fig.canvas.set_window_title('Clustering data from ' + URL)
# Show each element in the plots returned from plt.subplots()
for row, (row_label, X_x, X_y) in enumerate(Xs):
for col, (col_label, y_pred) in enumerate(predictions):
ax = plt.subplot(nrows, ncols, row * ncols + col + 1)
if row == 0:
plt.title(col_label)
if col == 0:
plt.ylabel(row_label)
# Plot the decomposed input data and use the predicted
# cluster index as the value in a color map.
plt.scatter(X_x, X_y, c=y_pred.astype(np.float), cmap='prism', alpha=0.5)
# Set the axis tick formatter to reduce the number of ticks
ax.xaxis.set_major_locator(MaxNLocator(nbins=4))
ax.yaxis.set_major_locator(MaxNLocator(nbins=4))
# Let matplotlib handle the subplot layout
plt.tight_layout()
# ==================================
# Display the plot in interactive UI
plt.show()
# To save the plot to an image file, use savefig()
#plt.savefig('plot.png')
# Open the image file with the default image viewer
#import subprocess
#subprocess.Popen('plot.png', shell=True)
# To save the plot to an image in memory, use BytesIO and savefig()
# This can then be written to any stream-like object, such as a
# file or HTTP response.
#from io import BytesIO
#img_stream = BytesIO()
#plt.savefig(img_stream, fmt='png')
#img_bytes = img_stream.getvalue()
#print('Image is {} bytes - {!r}'.format(len(img_bytes), img_bytes[:8] + b'...'))
# Closing the figure allows matplotlib to release the memory used.
plt.close()
# =====================================================================
if __name__ == '__main__':
# Download the data set from URL
print("Downloading data from {}".format(URL))
frame = download_data()
# Process data into a feature array
# This is unsupervised learning, and so there are no labels
print("Processing {} samples with {} attributes".format(len(frame.index), len(frame.columns)))
X = get_features(frame)
# Run multiple dimensionality reduction algorithms on the data
print("Reducing dimensionality")
Xs = list(reduce_dimensions(X))
# Evaluate multiple clustering learners on the data
print("Evaluating clustering learners")
predictions = list(evaluate_learners(X))
# Display the results
print("Plotting the results")
plot(Xs, predictions)
Python links
- Learn Python: https://pythonbasics.org/
- Python Tutorial: https://pythonprogramminglanguage.com