# Yet Another Blog in Statistical Computing

I can calculate the motion of heavenly bodies but not the madness of people. -Isaac Newton

## Parallelism with Joblib Package in Python

In the previous post (https://statcompute.wordpress.com/2015/12/27/import-csv-by-chunk-simultaneously-with-ipython-parallel), we’ve shown how to implement the parallelism with IPython parallel package. However, in that specific case, we were not able to observe the efficiency gain of parallelism.

In the example below, we tested Joblib package to implement the parallelism with Multiprocessing package as the back-end and searched for the optimal free parameter in a GRNN that has been demonstrated in (https://statcompute.wordpress.com/2015/12/09/fitting-generalized-regression-neural-network-with-python). As shown in the comparison below, CPU time of the parallel implementation with Joblib package is significantly shorter than CPU time of the serial implementation with map() function.

```In [1]: import pandas as pd

In [2]: import numpy as np

In [3]: from sklearn import preprocessing, cross_validation

In [4]: from neupy.algorithms import GRNN as grnn

In [5]: from neupy.functions import mse

In [6]: from joblib import Parallel, delayed

In [7]: df = pd.read_table("csdata.txt")

In [8]: y = df.ix[:, 0]

In [9]: x = df.ix[:, 1:df.shape[1]]

In [10]: st_x = preprocessing.scale(x)

In [11]: x_train, x_test, y_train, y_test = cross_validation.train_test_split(st_x, y, train_size = 0.6, random_state = 2016)

In [12]: def try_std(x):
....:       nn = grnn(std = x, verbose = False)
....:       nn.train(x_train, y_train)
....:       y_pred = nn.predict(x_test)
....:       print x, "-->", "{:10.8f}".format(mse(y_pred, y_test))
....:

In [13]: ### SERIAL IMPLEMENTATION ###

In [14]: %time map(try_std, np.linspace(0.5, 2.0, 16))
0.5 --> 0.03598864
0.6 --> 0.03387313
0.7 --> 0.03260287
0.8 --> 0.03188978
0.9 --> 0.03151914
1.0 --> 0.03134342
1.1 --> 0.03128110
1.2 --> 0.03129023
1.3 --> 0.03134819
1.4 --> 0.03143958
1.5 --> 0.03155242
1.6 --> 0.03167701
1.7 --> 0.03180485
1.8 --> 0.03192895
1.9 --> 0.03204561
2.0 --> 0.03215511
CPU times: user 7.15 s, sys: 11.8 s, total: 18.9 s
Wall time: 5.94 s

In [15]: ### PARALLEL IMPLEMENTATION ###

In [16]: %time Parallel(n_jobs = 8)(delayed(try_std)(i) for i in np.linspace(0.5, 2.0, 16))
0.5 --> 0.03598864
0.9 --> 0.03151914
0.6 --> 0.03387313
0.7 --> 0.03260287
1.2 --> 0.03129023
1.1 --> 0.03128110
0.8 --> 0.03188978
1.0 --> 0.03134342
1.3 --> 0.03134819
1.6 --> 0.03167701
1.8 --> 0.03192895
1.5 --> 0.03155242
1.9 --> 0.03204561
1.4 --> 0.03143958
1.7 --> 0.03180485
2.0 --> 0.03215511
CPU times: user 60.9 ms, sys: 270 ms, total: 331 ms
Wall time: 2.87 s

```
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Written by statcompute

December 30, 2015 at 1:45 am