altair: MaxRowsError for pandas.df with > 5000 rows

Hey,

Thanks for the package, I’m very keen to try it out on my own data. When trying to create a simple histogram with my own data, VegaLite fails on dataframes with more than 5000 rows. Here’s a minimal reproducible example:

import altair as alt
import os
import pandas as pd
import numpy as np

lengths = np.random.randint(0,2000,6000)
lengths_list = lengths.tolist()
labels = [str(i) for i in lengths_list]
peak_lengths = pd.DataFrame.from_dict({'coords': labels, 'length': lengths_list},orient='columns')
alt.Chart(peak_lengths).mark_bar().encode(alt.X('lengths:Q', bin=True),y='count(*):Q')

Here’s the error:

---------------------------------------------------------------------------
MaxRowsError                              Traceback (most recent call last)
~/anaconda/envs/py3/lib/python3.5/site-packages/altair/vegalite/v2/api.py in to_dict(self, *args, **kwargs)
    259         copy = self.copy()
    260         original_data = getattr(copy, 'data', Undefined)
--> 261         copy._prepare_data()
    262 
    263         # We make use of two context markers:

~/anaconda/envs/py3/lib/python3.5/site-packages/altair/vegalite/v2/api.py in _prepare_data(self)
    251             pass
    252         elif isinstance(self.data, pd.DataFrame):
--> 253             self.data = pipe(self.data, data_transformers.get())
    254         elif isinstance(self.data, six.string_types):
    255             self.data = core.UrlData(self.data)

~/anaconda/envs/py3/lib/python3.5/site-packages/toolz/functoolz.py in pipe(data, *funcs)
    550     """
    551     for func in funcs:
--> 552         data = func(data)
    553     return data
    554 

~/anaconda/envs/py3/lib/python3.5/site-packages/toolz/functoolz.py in __call__(self, *args, **kwargs)
    281     def __call__(self, *args, **kwargs):
    282         try:
--> 283             return self._partial(*args, **kwargs)
    284         except TypeError as exc:
    285             if self._should_curry(args, kwargs, exc):

~/anaconda/envs/py3/lib/python3.5/site-packages/altair/vegalite/data.py in default_data_transformer(data)
    122 @curry
    123 def default_data_transformer(data):
--> 124     return pipe(data, limit_rows, to_values)
    125 
    126 

~/anaconda/envs/py3/lib/python3.5/site-packages/toolz/functoolz.py in pipe(data, *funcs)
    550     """
    551     for func in funcs:
--> 552         data = func(data)
    553     return data
    554 

~/anaconda/envs/py3/lib/python3.5/site-packages/toolz/functoolz.py in __call__(self, *args, **kwargs)
    281     def __call__(self, *args, **kwargs):
    282         try:
--> 283             return self._partial(*args, **kwargs)
    284         except TypeError as exc:
    285             if self._should_curry(args, kwargs, exc):

~/anaconda/envs/py3/lib/python3.5/site-packages/altair/vegalite/data.py in limit_rows(data, max_rows)
     47             return data
     48     if len(values) > max_rows:
---> 49         raise MaxRowsError('The number of rows in your dataset is greater than the max of {}'.format(max_rows))
     50     return data
     51 

MaxRowsError: The number of rows in your dataset is greater than the max of 5000

A quick issues search didn’t turn up any hits for MaxRowsError. There is a related issue (#287), but this was a data set with > 300k rows, and I have a measly 35k. Also, the FAQ link referenced in that issue now turns up a 404. For the meantime, does the advice in #249 still apply?

Package info: Running on Altair 2.0.0rc1, JupyterLab 0.31.12-py35_1 conda-forge