fastdist 1.1.0

Faster distance calculations in python using numba

fastdist: Faster distance calculations in python using numba

fastdist is a replacement for scipy.spatial.distance that shows significant speed improvements by using numba and some optimization

Newer versions of fastdist (> 1.0.0) also add partial implementations of sklearn.metrics which also show significant speed improvements.

Along with adding several sklearn.metrics functions, fastdist 1.1.0 fixes an error in the Chebyshev distance calculation and adds slight speed optimizations.

Installation

Use the package manager pip to install fastdist.

pip install fastdist

Usage

For calculating the distance between 2 vectors, fastdist uses the same function calls as scipy.spatial.distance. So, for example, to calculate the Euclidean distance between 2 vectors, run:

from fastdist import fastdist
import numpy as np

u = np.random.rand(100)
v = np.random.rand(100)

fastdist.euclidean(u, v)

The same is true for most sklearn.metrics functions, though not all functions in sklearn.metrics are implemented in fastdist. Notably, most of the ROC-based functions are not (yet) available in fastdist. However, the other functions are the same as sklearn.metrics. So, for example, to create a confusion matrix from two discrete vectors, run:

from fastdist import fastdist
import numpy as np

y_true = np.random.randint(10, size=10000)
y_pred = np.random.randint(10, size=10000)

fastdist.confusion_matrix(y_true, y_pred)

For calculating distances involving matrices, fastdist has a few different functions instead of scipy's cdist and pdist.

To calculate the distance between a vector and each row of a matrix, use vector_to_matrix_distance:

from fastdist import fastdist
import numpy as np

u = np.random.rand(100)
m = np.random.rand(50, 100)

fastdist.vector_to_matrix_distance(u, m, fastdist.euclidean, "euclidean")
# returns an array of shape (50,)

To calculate the distance between the rows of 2 matrices, use matrix_to_matrix_distance:

from fastdist import fastdist
import numpy as np

a = np.random.rand(25, 100)
b = np.random.rand(50, 100)

fastdist.matrix_to_matrix_distance(a, b, fastdist.euclidean, "euclidean")
# returns an array of shape (25, 50)

Finally, to calculate the pairwise distances between the rows of a matrix, use matrix_pairwise_distance:

from fastdist import fastdist
import numpy as np

a = np.random.rand(10, 100)
fastdist.matrix_pairwise_distance(a, fastdist.euclidean, "euclidean", return_matrix=False)
# returns an array of shape (10 choose 2, 1)
# to return a matrix with entry (i, j) as the distance between row i and j
# set return_matrix=True, in which case this will return a (10, 10) array

Speed

fastdist is significantly faster than scipy.spatial.distance in most cases.

Though almost all functions will show a speed improvement in fastdist, certain functions will have an especially large improvement. Notably, cosine similarity is much faster, as are the vector/matrix, matrix/matrix, and pairwise matrix calculations.

Note that numba - the primary package fastdist uses - compiles the function to machine code the first time it is called. So, the first time you call a function will be slower than the following times, as the first runtime includes the compile time.

Here are some examples comparing the speed of fastdist to scipy.spatial.distance:

from fastdist import fastdist
import numpy as np
from scipy.spatial import distance

a, b = np.random.rand(200, 100), np.random.rand(2500, 100)
%timeit -n 100 fastdist.matrix_to_matrix_distance(a, b, fastdist.cosine, "cosine")
# 8.97 ms ± 11.2 ms per loop (mean ± std. dev. of 7 runs, 100 loops each)
# note this high stdev is because of the first run taking longer to compile

%timeit -n 100 distance.cdist(a, b, "cosine")
# 57.9 ms ± 4.43 ms per loop (mean ± std. dev. of 7 runs, 100 loops each)

In this example, fastdist is about 7x faster than scipy.spatial.distance. This difference only gets larger as the matrices get bigger and when we compile the fastdist function once before running it. For example:

from fastdist import fastdist
import numpy as np
from scipy.spatial import distance

a, b = np.random.rand(200, 1000), np.random.rand(2500, 1000)
# i complied the matrix_to_matrix function once before this so it's already in machine code
%timeit fastdist.matrix_to_matrix_distance(a, b, fastdist.cosine, "cosine")
# 25.4 ms ± 1.36 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

%timeit distance.cdist(a, b, "cosine")
# 689 ms ± 10.3 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)

Here, fastdist is about 27x faster than scipy.spatial.distance. Though cosine similarity is particularly optimized, other functions are still faster with fastdist. For example:

from fastdist import fastdist
import numpy as np
from scipy.spatial import distance

a = np.random.rand(200, 1000)

%timeit fastdist.matrix_pairwise_distance(a, fastdist.euclidean, "euclidean")
# 14 ms ± 458 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit distance.pdist(a, "euclidean")
# 26.9 ms ± 1.27 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

fastdist's implementation of the functions in sklearn.metrics are also significantly faster. For example:

from fastdist import fastdist
import numpy as np
from sklearn import metrics

y_true = np.random.randint(2, size=100000)
y_pred = np.random.randint(2, size=100000)

%timeit fastdist.accuracy_score(y_true, y_pred)
# 74 µs ± 5.81 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit metrics.accuracy_score(y_true, y_pred)
# 7.23 ms ± 157 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

Here, fastdist is about 97x faster than sklearn's implementation.