[transform_filter] - condition not working

I do not understand why the condition in transform_filter is not working and have not found any explanation around (including documentation).

1. The problem seems to be in FilterTransoform method.

2. another issue: where and how am I supposed to put/write the ‘background’ to change the default transparent?

import altair.vegalite.v2 as alt
import pandas as pd

stocks = pd.read_csv(data.stocks.url)
type(stocks)
stocks.head()
stocks.symbol
stocks['symbol'] = stocks['symbol'].astype('category') # forced to be a factor
stocks.symbol

base = alt.Chart(stocks).encode(
    x='date:T',
    y='price:Q',
    color='symbol:N'
).transform_filter(
    stocks.symbol == 'GOOG' # problem is here
)
base.mark_line()

[jakevdp]

Another thing (I should really read questions more carefully before answering 😄)

You’re rendering your plot with Vega-Lite version 1; this doesn’t support everything that Altair version 2 supports, and so filter transforms, background configurations, etc. will not always work properly, and some specifications will simply fail to produce a chart at all.

nteract does not support Vega-Lite 2 yet, and so I would not recommend it as a frontend for Altair at this time. You might try JupyterLab, Jupyter Notebook, or CoLab, until the nteract project updates its dependencies.

[jakevdp]

Oh, noticed your other question about backgrounds. If you want to configure the background, you can use:

Chart().configure(
    background='white'
)

The background is transparent by default, as mentioned here: https://vega.github.io/vega-lite/docs/config.html#top-level-config