:crown: Python factor analysis library (PCA, CA, MCA, MFA, FAMD)
Prince is a library for doing factor analysis. This includes a variety of methods including principal component analysis (PCA) and correspondence analysis (CA). The goal is to provide an efficient implementation for each algorithm along with a scikit-learn API.
:warning: Prince is only compatible with Python 3.
:snake: Although it isn't a requirement, using Anaconda is highly recommended.
Via PyPI
$ pip install prince
Via GitHub for the latest development version
$ pip install git+https://github.com/MaxHalford/Prince
Prince doesn't have any extra dependencies apart from the usual suspects (
sklearn,
pandas,
matplotlib) which are included with Anaconda.
import numpy as np; np.random.set_state(42) # this is for doctests reproducibility
Each estimator provided by
princeextends scikit-learn's
TransformerMixin. This means that each estimator implements a
fitand a
transformmethod which makes them usable in a transformation pipeline. The
fitmethod is actually an alias for the
row_principal_componentsmethod which returns the row principal components. However you can also access the column principal components with the
column_principal_components.
Under the hood Prince uses a randomised version of SVD. This is much faster than using the more commonly full approach. However the results may have a small inherent randomness. For most applications this doesn't matter and you shouldn't have to worry about it. However if you want reproducible results then you should set the
random_stateparameter.
The randomised version of SVD is an iterative method. Because each of Prince's algorithms use SVD, they all possess a
n_iterparameter which controls the number of iterations used for computing the SVD. On the one hand the higher
n_iteris the more precise the results will be. On the other hand increasing
n_iterincreases the computation time. In general the algorithm converges very quickly so using a low
n_iter(which is the default behaviour) is recommended.
You are supposed to use each method depending on your situation:
prince.PCA)
prince.CA)
prince.MCA)
prince.MFA)
prince.FAMD)
The next subsections give an overview of each method along with usage information. The following papers give a good overview of the field of factor analysis if you want to go deeper:
If you're using PCA it is assumed you have a dataframe consisting of numerical continuous variables. In this example we're going to be using the Iris flower dataset.
>>> import pandas as pd >>> import prince >>> from sklearn import datasets>>> X, y = datasets.load_iris(return_X_y=True) >>> X = pd.DataFrame(data=X, columns=['Sepal length', 'Sepal width', 'Petal length', 'Petal width']) >>> y = pd.Series(y).map({0: 'Setosa', 1: 'Versicolor', 2: 'Virginica'}) >>> X.head() Sepal length Sepal width Petal length Petal width 0 5.1 3.5 1.4 0.2 1 4.9 3.0 1.4 0.2 2 4.7 3.2 1.3 0.2 3 4.6 3.1 1.5 0.2 4 5.0 3.6 1.4 0.2
The
PCAclass implements scikit-learn's
fit/
transformAPI. It's parameters have to passed at initialisation before calling the
fitmethod.
>>> pca = prince.PCA( ... n_components=2, ... n_iter=3, ... rescale_with_mean=True, ... rescale_with_std=True, ... copy=True, ... check_input=True, ... engine='auto', ... random_state=42 ... ) >>> pca = pca.fit(X)
The available parameters are:
n_components: the number of components that are computed. You only need two if your intention is to make a chart.
n_iter: the number of iterations used for computing the SVD
rescale_with_mean: whether to substract each column's mean
rescale_with_std: whether to divide each column by it's standard deviation
copy: if
Falsethen the computations will be done inplace which can have possible side-effects on the input data
engine: what SVD engine to use (should be one of
['auto', 'fbpca', 'sklearn'])
random_state: controls the randomness of the SVD results.
Once the
PCAhas been fitted, it can be used to extract the row principal coordinates as so:
>>> pca.transform(X).head() # same as pca.row_coordinates(X).head() 0 1 0 -2.264703 0.480027 1 -2.080961 -0.674134 2 -2.364229 -0.341908 3 -2.299384 -0.597395 4 -2.389842 0.646835
Each column stands for a principal component whilst each row stands a row in the original dataset. You can display these projections with the
plot_row_coordinatesmethod:
>>> ax = pca.plot_row_coordinates( ... X, ... ax=None, ... figsize=(6, 6), ... x_component=0, ... y_component=1, ... labels=None, ... color_labels=y, ... ellipse_outline=False, ... ellipse_fill=True, ... show_points=True ... ) >>> ax.get_figure().savefig('images/pca_row_coordinates.svg')
Each principal component explains part of the underlying of the distribution. You can see by how much by using the accessing the
explained_inertia_property:
>>> pca.explained_inertia_ array([0.72962445, 0.22850762])
The explained inertia represents the percentage of the inertia each principal component contributes. It sums up to 1 if the
n_componentsproperty is equal to the number of columns in the original dataset. you The explained inertia is obtained by dividing the eigenvalues obtained with the SVD by the total inertia, both of which are also accessible.
>>> pca.eigenvalues_ array([2.91849782, 0.91403047])>>> pca.total_inertia_ 4.000000...
>>> pca.explained_inertia_ array([0.72962445, 0.22850762])
You can also obtain the correlations between the original variables and the principal components.
>>> pca.column_correlations(X) 0 1 Petal length 0.991555 0.023415 Petal width 0.964979 0.064000 Sepal length 0.890169 0.360830 Sepal width -0.460143 0.882716
You may also want to know how much each observation contributes to each principal component. This can be done with the
row_contributionsmethod.
>>> pca.row_contributions(X).head() 0 1 0 1.757369 0.252098 1 1.483777 0.497200 2 1.915225 0.127896 3 1.811606 0.390447 4 1.956947 0.457748
You can also transform row projections back into their original space by using the
inverse_transformmethod.
>>> pca.inverse_transform(pca.transform(X)).head() 0 1 2 3 0 5.018949 3.514854 1.466013 0.251922 1 4.738463 3.030433 1.603913 0.272074 2 4.720130 3.196830 1.328961 0.167414 3 4.668436 3.086770 1.384170 0.182247 4 5.017093 3.596402 1.345411 0.206706
You should be using correspondence analysis when you want to analyse a contingency table. In other words you want to analyse the dependencies between two categorical variables. The following example comes from section 17.2.3 of this textbook. It shows the number of occurrences between different hair and eye colors.
>>> import pandas as pd>>> pd.set_option('display.float_format', lambda x: '{:.6f}'.format(x)) >>> X = pd.DataFrame( ... data=[ ... [326, 38, 241, 110, 3], ... [688, 116, 584, 188, 4], ... [343, 84, 909, 412, 26], ... [98, 48, 403, 681, 85] ... ], ... columns=pd.Series(['Fair', 'Red', 'Medium', 'Dark', 'Black']), ... index=pd.Series(['Blue', 'Light', 'Medium', 'Dark']) ... ) >>> X Fair Red Medium Dark Black Blue 326 38 241 110 3 Light 688 116 584 188 4 Medium 343 84 909 412 26 Dark 98 48 403 681 85
Unlike the
PCAclass, the
CAonly exposes scikit-learn's
fitmethod.
>>> import prince >>> ca = prince.CA( ... n_components=2, ... n_iter=3, ... copy=True, ... check_input=True, ... engine='auto', ... random_state=42 ... ) >>> X.columns.rename('Hair color', inplace=True) >>> X.index.rename('Eye color', inplace=True) >>> ca = ca.fit(X)
The parameters and methods overlap with those proposed by the
PCAclass.
>>> ca.row_coordinates(X) 0 1 Blue -0.400300 -0.165411 Light -0.440708 -0.088463 Medium 0.033614 0.245002 Dark 0.702739 -0.133914>>> ca.column_coordinates(X) 0 1 Fair -0.543995 -0.173844 Red -0.233261 -0.048279 Medium -0.042024 0.208304 Dark 0.588709 -0.103950 Black 1.094388 -0.286437
You can plot both sets of principal coordinates with the
plot_coordinatesmethod.
>>> ax = ca.plot_coordinates( ... X=X, ... ax=None, ... figsize=(6, 6), ... x_component=0, ... y_component=1, ... show_row_labels=True, ... show_col_labels=True ... ) >>> ax.get_figure().savefig('images/ca_coordinates.svg')
Like for the
PCAyou can access the inertia contribution of each principal component as well as the eigenvalues and the total inertia.
>>> ca.eigenvalues_ [0.199244..., 0.030086...]>>> ca.total_inertia_ 0.230191...
>>> ca.explained_inertia_ [0.865562..., 0.130703...]
Multiple correspondence analysis (MCA) is an extension of correspondence analysis (CA). It should be used when you have more than two categorical variables. The idea is simply to compute the one-hot encoded version of a dataset and apply CA on it. As an example we're going to use the balloons dataset taken from the UCI datasets website.
>>> import pandas as pd>>> X = pd.read_csv('https://archive.ics.uci.edu/ml/machine-learning-databases/balloons/adult+stretch.data') >>> X.columns = ['Color', 'Size', 'Action', 'Age', 'Inflated'] >>> X.head() Color Size Action Age Inflated 0 YELLOW SMALL STRETCH ADULT T 1 YELLOW SMALL STRETCH CHILD F 2 YELLOW SMALL DIP ADULT F 3 YELLOW SMALL DIP CHILD F 4 YELLOW LARGE STRETCH ADULT T
The
MCAalso implements the
fitand
transformmethods.
>>> import prince >>> mca = prince.MCA( ... n_components=2, ... n_iter=3, ... copy=True, ... check_input=True, ... engine='auto', ... random_state=42 ... ) >>> mca = mca.fit(X)
Like the
CAclass, the
MCAclass also has
plot_coordinatesmethod.
>>> ax = mca.plot_coordinates( ... X=X, ... ax=None, ... figsize=(6, 6), ... show_row_points=True, ... row_points_size=10, ... show_row_labels=False, ... show_column_points=True, ... column_points_size=30, ... show_column_labels=False, ... legend_n_cols=1 ... ) >>> ax.get_figure().savefig('images/mca_coordinates.svg')
The eigenvalues and inertia values are also accessible.
>>> mca.eigenvalues_ [0.401656..., 0.211111...]>>> mca.total_inertia_ 1.0
>>> mca.explained_inertia_ [0.401656..., 0.211111...]
Multiple factor analysis (MFA) is meant to be used when you have groups of variables. In practice it builds a PCA on each group -- or an MCA, depending on the types of the group's variables. It then constructs a global PCA on the results of the so-called partial PCAs -- or MCAs. The dataset used in the following examples come from this paper. In the dataset, three experts give their opinion on six different wines. Each opinion for each wine is recorded as a variable. We thus want to consider the separate opinions of each expert whilst also having a global overview of each wine. MFA is the perfect fit for this kind of situation.
First of all let's copy the data used in the paper.
>>> import pandas as pd>>> X = pd.DataFrame( ... data=[ ... [1, 6, 7, 2, 5, 7, 6, 3, 6, 7], ... [5, 3, 2, 4, 4, 4, 2, 4, 4, 3], ... [6, 1, 1, 5, 2, 1, 1, 7, 1, 1], ... [7, 1, 2, 7, 2, 1, 2, 2, 2, 2], ... [2, 5, 4, 3, 5, 6, 5, 2, 6, 6], ... [3, 4, 4, 3, 5, 4, 5, 1, 7, 5] ... ], ... columns=['E1 fruity', 'E1 woody', 'E1 coffee', ... 'E2 red fruit', 'E2 roasted', 'E2 vanillin', 'E2 woody', ... 'E3 fruity', 'E3 butter', 'E3 woody'], ... index=['Wine {}'.format(i+1) for i in range(6)] ... ) >>> X['Oak type'] = [1, 2, 2, 2, 1, 1]
The groups are passed as a dictionary to the
MFAclass.
>>> groups = { ... 'Expert #{}'.format(no+1): [c for c in X.columns if c.startswith('E{}'.format(no+1))] ... for no in range(3) ... } >>> import pprint >>> pprint.pprint(groups) {'Expert #1': ['E1 fruity', 'E1 woody', 'E1 coffee'], 'Expert #2': ['E2 red fruit', 'E2 roasted', 'E2 vanillin', 'E2 woody'], 'Expert #3': ['E3 fruity', 'E3 butter', 'E3 woody']}
Now we can fit an
MFA.
>>> import prince >>> mfa = prince.MFA( ... groups=groups, ... n_components=2, ... n_iter=3, ... copy=True, ... check_input=True, ... engine='auto', ... random_state=42 ... ) >>> mfa = mfa.fit(X)
The
MFAinherits from the
PCAclass, which entails that you have access to all it's methods and properties. The
row_coordinatesmethod will return the global coordinates of each wine.
>>> mfa.row_coordinates(X) 0 1 Wine 1 -2.172155 -0.508596 Wine 2 0.557017 -0.197408 Wine 3 2.317663 -0.830259 Wine 4 1.832557 0.905046 Wine 5 -1.403787 0.054977 Wine 6 -1.131296 0.576241
Just like for the
PCAyou can plot the row coordinates with the
plot_row_coordinatesmethod.
>>> ax = mfa.plot_row_coordinates( ... X, ... ax=None, ... figsize=(6, 6), ... x_component=0, ... y_component=1, ... labels=X.index, ... color_labels=['Oak type {}'.format(t) for t in X['Oak type']], ... ellipse_outline=False, ... ellipse_fill=True, ... show_points=True ... ) >>> ax.get_figure().savefig('images/mfa_row_coordinates.svg')
You can also obtain the row coordinates inside each group. The
partial_row_coordinatesmethod returns a
pandas.DataFramewhere the set of columns is a
pandas.MultiIndex. The first level of indexing corresponds to each specified group whilst the nested level indicates the coordinates inside each group.
>>> mfa.partial_row_coordinates(X) # doctest: +NORMALIZE_WHITESPACE Expert #1 Expert #2 Expert #3 0 1 0 1 0 1 Wine 1 -2.764432 -1.104812 -2.213928 -0.863519 -1.538106 0.442545 Wine 2 0.773034 0.298919 0.284247 -0.132135 0.613771 -0.759009 Wine 3 1.991398 0.805893 2.111508 0.499718 2.850084 -3.796390 Wine 4 1.981456 0.927187 2.393009 1.227146 1.123206 0.560803 Wine 5 -1.292834 -0.620661 -1.492114 -0.488088 -1.426414 1.273679 Wine 6 -0.688623 -0.306527 -1.082723 -0.243122 -1.622541 2.278372
Likewhise you can visualize the partial row coordinates with the
plot_partial_row_coordinatesmethod.
>>> ax = mfa.plot_partial_row_coordinates( ... X, ... ax=None, ... figsize=(6, 6), ... x_component=0, ... y_component=1, ... color_labels=['Oak type {}'.format(t) for t in X['Oak type']] ... ) >>> ax.get_figure().savefig('images/mfa_partial_row_coordinates.svg')
As usual you have access to inertia information.
>>> mfa.eigenvalues_ array([0.47246678, 0.05947651])>>> mfa.total_inertia_ 0.558834...
>>> mfa.explained_inertia_ array([0.84545097, 0.10642965])
You can also access information concerning each partial factor analysis via the
partial_factor_analysis_attribute.
>>> for name, fa in sorted(mfa.partial_factor_analysis_.items()): ... print('{} eigenvalues: {}'.format(name, fa.eigenvalues_)) Expert #1 eigenvalues: [0.47709918 0.01997272] Expert #2 eigenvalues: [0.60851399 0.03235984] Expert #3 eigenvalues: [0.41341481 0.07353257]
The
row_contributionsmethod will provide you with the inertia contribution of each row with respect to each component.
>>> mfa.row_contributions(X) 0 1 Wine 1 9.986433 4.349104 Wine 2 0.656699 0.655218 Wine 3 11.369187 11.589968 Wine 4 7.107942 13.771950 Wine 5 4.170915 0.050817 Wine 6 2.708824 5.582943
The
column_correlationsmethod will return the correlation between the original variables and the components.
>>> mfa.column_correlations(X) 0 1 E1 coffee -0.918449 -0.043444 E1 fruity 0.968449 0.192294 E1 woody -0.984442 -0.120198 E2 red fruit 0.887263 0.357632 E2 roasted -0.955795 0.026039 E2 vanillin -0.950629 -0.177883 E2 woody -0.974649 0.127239 E3 butter -0.945767 0.221441 E3 fruity 0.594649 -0.820777 E3 woody -0.992337 0.029747
A description is on it's way. This section is empty because I have to refactor the documentation a bit.
>>> import pandas as pd>>> X = pd.DataFrame( ... data=[ ... ['A', 'A', 'A', 2, 5, 7, 6, 3, 6, 7], ... ['A', 'A', 'A', 4, 4, 4, 2, 4, 4, 3], ... ['B', 'A', 'B', 5, 2, 1, 1, 7, 1, 1], ... ['B', 'A', 'B', 7, 2, 1, 2, 2, 2, 2], ... ['B', 'B', 'B', 3, 5, 6, 5, 2, 6, 6], ... ['B', 'B', 'A', 3, 5, 4, 5, 1, 7, 5] ... ], ... columns=['E1 fruity', 'E1 woody', 'E1 coffee', ... 'E2 red fruit', 'E2 roasted', 'E2 vanillin', 'E2 woody', ... 'E3 fruity', 'E3 butter', 'E3 woody'], ... index=['Wine {}'.format(i+1) for i in range(6)] ... ) >>> X['Oak type'] = [1, 2, 2, 2, 1, 1]
Now we can fit an
FAMD.
>>> import prince >>> famd = prince.FAMD( ... n_components=2, ... n_iter=3, ... copy=True, ... check_input=True, ... engine='auto', ... random_state=42 ... ) >>> famd = famd.fit(X.drop('Oak type', axis='columns'))
The
FAMDinherits from the
MFAclass, which entails that you have access to all it's methods and properties. The
row_coordinatesmethod will return the global coordinates of each wine.
>>> famd.row_coordinates(X) 0 1 Wine 1 -1.488689 -1.002711 Wine 2 -0.449783 -1.354847 Wine 3 1.774255 -0.258528 Wine 4 1.565402 0.016484 Wine 5 -0.349655 1.516425 Wine 6 -1.051531 1.083178
Just like for the
MFAyou can plot the row coordinates with the
plot_row_coordinatesmethod.
>>> ax = famd.plot_row_coordinates( ... X, ... ax=None, ... figsize=(6, 6), ... x_component=0, ... y_component=1, ... labels=X.index, ... color_labels=['Oak type {}'.format(t) for t in X['Oak type']], ... ellipse_outline=False, ... ellipse_fill=True, ... show_points=True ... ) >>> ax.get_figure().savefig('images/famd_row_coordinates.svg')
By default
princeuses
sklearn's randomized SVD implementation (the one used under the hood for
TruncatedSVD). One of the goals of Prince is to make it possible to use a different SVD backend. For the while the only other supported backend is Facebook's randomized SVD implementation called fbpca. You can use it by setting the
engineparameter to
'fbpca':
>>> import prince >>> pca = prince.PCA(engine='fbpca')
If you are using Anaconda then you should be able to install
fbpcawithout any pain by running
pip install fbpca.
The MIT License (MIT). Please see the license file for more information.