Interesting performance comparisons between pandas and numpy

Pandas and Numpy are two packages that are core to a lot of data analysis. In this post I will compare the performance of numpy and pandas.

tl;dr:

`numpy`

consumes less memory compared to`pandas`

`numpy`

generally performs better than`pandas`

for 50K rows or less`pandas`

generally performs better than`numpy`

for 500K rows or more- for 50K to 500K rows, it is a toss up between
`pandas`

and`numpy`

depending on the kind of operation

In [1]:

```
import pandas as pd
import matplotlib.pyplot as plt
plt.style.use("seaborn-pastel")
%matplotlib inline
import seaborn.apionly as sns
import numpy as np
from timeit import timeit
import sys
```

In [2]:

```
iris = sns.load_dataset('iris')
```

In [3]:

```
data = pd.concat([iris]*100000)
data_rec = data.to_records()
```

In [4]:

```
print (len(data), len(data_rec))
```

`iris`

dataset and replicated it so as to have 15MM rows of data. The space requirement for 15MM rows of data in a `pandas dataframe`

is more than twice that of a `numpy recarray`

.

In [5]:

```
MB = 1024*1024
print("Pandas %d MB " % (sys.getsizeof(data)/MB))
print("Numpy %d MB " % (sys.getsizeof(data_rec)/MB))
```

A snippet of the data shown below.

In [6]:

```
data.head()
```

Out[6]:

In [7]:

Expand Code

In this post, performance metrics for a few different categories are compared between `numpy`

and `pandas`

:

- operations on a column of data, such as mean or applying a vectorised function
- operations on a filtered column of data
- vector operations on a column or filtered column

`mean`

, vectorised `log`

or a string based `unique`

operation. All these are `O(n)`

calculations. The mean calculation is orders of magnitude faster in `numpy`

compared to `pandas`

for array sizes of 100K or less. For sizes larger than 100K `pandas`

maintains a lead over `numpy`

.

In [8]:

```
bench(data, "data.loc[:, 'sepal_length'].mean()",
data_rec, "np.mean(data_rec.sepal_length)",
title="Mean on Unfiltered Column")
```

`log`

operation is faster in `numpy`

for sizes less than 100K but pandas costs about the same for sizes larger than 100K.

In [9]:

```
bench(data, "np.log(data.loc[:, 'sepal_length'])",
data_rec, "np.log(data_rec.sepal_length)",
title="Vectorised log on Unfiltered Column")
```

`species`

is of string type. The operation demonstrated is a `unique`

calculation. We observe that the `unique`

calculation is roughly an order of magnitude faster in pandas for sizes larger than 1K rows.

In [10]:

```
bench(data, "data.loc[:,'species'].unique()",
data_rec, "np.unique(data_rec.species)",
grid=np.array([100, 1000, 10000, 100000, 1000000]),
title="Unique on Unfiltered String Column")
```

Below we perform the same tests as above, except that the column is not a full view, but is instead a filtered view. The filters are simple filters with an arithmetic bool comparison for the first two and a string comparison for the third below.

Below, `mean`

is calculated for a filtered column `sepal_length`

. Here performance of `pandas`

is better for row sizes larger than 10K. In the `mean`

on unfiltered column shown above, `pandas`

performed better for 1MM or more. Just having selection operations has shifted performance chart in favor of `pandas`

for even smaller number of records.

In [11]:

```
bench(data, "data.loc[(data.sepal_width>3) & \
(data.petal_length<1.5), 'sepal_length'].mean()",
data_rec, "np.mean(data_rec[(data_rec.sepal_width>3) & \
(data_rec.petal_length<1.5)].sepal_length)",
grid=np.array([1000, 10000, 100000, 1000000]),
title="Mean on Filtered Column")
```

`log`

operation on a unfiltered column shown above, `numpy`

performed better than `pandas`

for number of records less than 100K while the performance was comparable for the two for sizes larger than 100K. But the moment you introduce a filter on a column, `pandas`

starts to show an edge over `numpy`

for number of records larger than 10K.

In [12]:

```
bench(data, "np.log(data.loc[(data.sepal_width>3) & \
(data.petal_length<1.5), 'sepal_length'])",
data_rec, "np.log(data_rec[(data_rec.sepal_width>3) & \
(data_rec.petal_length<1.5)].sepal_length)",
grid=np.array([1000, 10000, 100000, 1000000]),
title="Vectorised log on Filtered Column")
```

`mean`

reduction on a column but with a string filter. We see a similar behavior where `numpy`

performs significantly better at small sizes and `pandas`

takes a gentle lead for larger number of records.

In [13]:

```
bench(data, "data[data.species=='setosa'].sepal_length.mean()",
data_rec, "np.mean(data_rec[data_rec.species=='setosa'].sepal_length)",
grid=np.array([1000, 10000, 100000, 1000000]),
title="Mean on (String) Filtered Column")
```

`pandas`

has a slight edge over `numpy`

for large number of records. For smaller than 100K records, `numpy`

performs significantly better.

In [14]:

```
bench(data, "data.petal_length * data.sepal_length + \
data.petal_width * data.sepal_width",
data_rec, "data_rec.petal_length*data_rec.sepal_length + \
data_rec.petal_width * data_rec.sepal_width",
title="Vectorised Math on Unfiltered Columns")
```

`mean`

reduction is computed on the filtered column. The presence of a filter makes `pandas`

significantly faster for sizes larger than 100K, while `numpy`

maitains a lead for smaller than 10K number of records.

In [16]:

```
bench(data, "data.loc[data.sepal_width * data.petal_length > \
data.sepal_length, 'sepal_length'].mean()",
data_rec, "np.mean(data_rec[data_rec.sepal_width * data_rec.petal_length \
> data_rec.sepal_length].sepal_length)",
title="Vectorised Math in Filtering Columns",
grid=np.array([100, 1000, 10000, 100000, 1000000]))
```

`Pandas`

is often used in an interactive environment such as through Jupyter notebooks. In such a case, any performance loss from `pandas`

will be in significant. But if you have smaller `pandas`

dataframes (<50K number of records) in a production environment, then it is worth considering `numpy`

recarrays.

`numpy`

consumes (roughtly 1/3) less memory compared to`pandas`

`numpy`

generally performs better than`pandas`

for 50K rows or less`pandas`

generally performs better than`numpy`

for 500K rows or more- for 50K to 500K rows, it is a toss up between
`pandas`

and`numpy`

depending on the kind of operation

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