Generate random data for testing a pandas dataframe with hypothesis

Question

I am working a lot of pandas dataframes and I want to test them using pytest and I am using hypothesis to generate the test data.

The issues I am having is that it is generating the same data values in each column.

I actually don't know how to generate real data to test with ..

Here is what I am trying :

from hypothesis.extra.pandas import data_frames , column, range_indexes
from hypothesis import given, settings, strategies as st
import pandas as pd
from datetime import datetime

data = data_frames(columns=[column(name='key',  elements=st.floats(allow_nan=True)),
                                          column(name='fbms_start_date', elements=st.datetimes(min_value=datetime(2020, 7, 1),
                                                                                               max_value=datetime.now())),
                                          column(name='breakdown_type', elements=st.just("Total")),
                                          column(name='breakdown_one', elements=st.just(float('nan'))),
                                          column(name='adset_id', elements=st.floats(allow_nan=True)),
                                          column(name='adset_name', elements=st.text()),
                                          column(name='campaign_id', elements=st.floats(allow_nan=True, )),
                                          column(name='campaign_name', elements=st.text()),
                                          column(name='reach', elements=st.text()),
                                          column(name='impressions', elements=st.just(float('nan'))),
                                          column(name='spend', elements=st.floats(allow_nan=False)),
                                          column(name='page_likes', elements=st.floats(allow_nan=False)),
                                          column(name='post_engagement', elements=st.sampled_from(['LINK_CLICKS', 
                                                                                                        'POST_ENGAGEMENT', 
                                                                                                        'PAGE_LIKES'])),
                                          column(name='objective', elements=st.floats(allow_nan=False)),
                                          column(name='ads_run', elements=st.sampled_from([True, False]))],
                                          index=range_indexes(min_size=100)
                                        ) 

@given(df=data)
@settings(max_examples=5)
def test_hyothesis(df):
    print(df)
    assert 1

this is always generating the following dataset

key fbms_start_date breakdown_type  breakdown_one   adset_id    adset_name  campaign_id campaign_name   reach   impressions spend   page_likes  post_engagement objective   ads_run
0   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
1   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
2   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
3   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
4   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
5   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
6   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
7   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
8   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True
9   0.0 2020-07-01  Total       0.0     0.0             0.0 0.0 LINK_CLICKS 0.0 True

And as you can see for that each colunms have one values not unique values , I don't know how to generate real values I can test with ..

Any help will be helpful...

Thank for this commentt , I thought about that but the issues is that those dates should not be unique — Espoir Murhabazi
– Espoir Murhabazi, Commented Jan 13, 2021 at 20:08

Espoir Murhabazi · Accepted Answer · 2021-01-14 13:41:39Z

Zac gives some good insight in his answer and from that, I understood why I was getting the issue, I managed to have some data with the code I shared with some hack from the documentation. Although it is not generating 100% of what I wanted it was enough for the testing.

Here is how I generated the columns and afterward the data.

I use the following code to define the columns strategies :

from hypothesis.extra.pandas import data_frames , column, range_indexes
from hypothesis import strategies as st, given, settings
import pandas as pd
from datetime import datetime

datetime_st = st.dates(
    min_value=datetime(2020, 7, 1).date(),
    max_value=datetime.today().date()
)


float_without_nan_st = st.floats(min_value=0.0001, max_value=3030, allow_nan=False)
float_with_nan_st = st.floats(allow_nan=True, allow_infinity=False)
text_st = st.text(alphabet="espoiristusingacolemakeyboard", min_size=5)
boolean_st = st.boolean()

Then I created the dataframes with :

df_columns = {
    "fbms_start_date": {"elements": datetime_st, "unique": True},
    "fbmb_spend": {"elements": float_without_nan_st, "unique":True},
    "fbmb_adset_id": {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
    "fbmb_adset_name": {"elements": text_st, "unique":False, "fill": st.nothing()}, 
    "fbmb_ads_run": {"elements": boolean_st},
    "fbms_key" : {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
    "fbmb_breakdown_type": {"elements": st.just("Total")},
    "fbmb_breakdown_one": {"elements": st.just(float('nan')) }, 
    "fbmb_campaign_id": {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
    "fbmb_campaign_name" : {"elements": text_st, "unique":False, "fill": st.nothing()},
    "fbmb_reach" : {"elements": text_st, "unique":False, "fill": st.nothing()},
    "fbmb_impressions" : {"elements": st.integers(min_value=0, max_value=100001) },
    "fbmb_spend" : {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
    "fbmb_page_likes" : {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
    "fbmb_post_engagement" : {"elements": st.sampled_from(['LINK_CLICKS', 
                                                            'POST_ENGAGEMENT', 
                                                            'PAGE_LIKES']), "unique":False},
    "fbmb_objective" : {"elements": float_with_nan_st, "unique":False, "fill": st.nothing()},
}

Next I generated my dataset with :

test_dfs = data_frames(
    index=range_indexes(min_size=10),
    columns=[column(key, **value) for key, value in df_columns.items()],
)

And finally, I was able to run the following tests

@given(df=test_dfs)
@settings(max_examples=5)
def test_hyothesis(df):
    print(df)
    assert 1

Note the min_size in the index from the dataset generation and the max_example in the settings.

Zac Hatfield-Dodds · Accepted Answer · 2021-01-14 03:37:09Z

2

The first example is because Hypothesis always starts by generating the simplest possible example, which will be all-zeros (etc.). I'd recommend turning up the max_examples setting - the default 100 is good, but less than 20 is very very few.

You've also specified a very large min_size=100 for your index - is it really impossible to have a failing example with fewer rows? If not, set it much smaller - Hypothesis is great a finding bugs with small inputs, and they're way faster to generate too.

Completing our set of causes, Hypothesis generates dataframes with a "fill value" for each column - and at this large size and few examples, when you only see the first few and last few rows all you're looking at is the minimal fill-value. Set min_size=1 and this problem will go away entirely.

answered Jan 14, 2021 at 3:37

Zac Hatfield-Dodds

3,1929 silver badges26 bronze badges

1 Comment

Espoir Murhabazi Over a year ago

Thanks @zac for this .. I think I am getting what I was missing let me implement it and I will tell you how it goes

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