Repeated values in date axis

[lucasbalponti]

Hello guys!

I'm trying to make a bar graph which has its X axis's type as time. I formatted it using 'utcyearmonth', but the X axis's label repeats values.

Is it a bug? Is there a way to solve it?

This is what happens to the graph

The code I've written is:

serie_temporal = alt.Chart(base_filtrada).mark_bar(size=60).encode(
    x=alt.X(
        'utcyearmonth(Data):T', 
        axis=alt.Axis(format="%Y %B"),
        scale = alt.Scale(nice={'interval': 'month', 'step': 1})
    ),
    y='sum(Valor):Q',
    color='Tipo de despesa'
).properties(
    height=400
)

I already tried changing the axis type from time to nominal, ordinal and quantitative and removing the scale configuration.

Thank you in advance!

[ChristopherDavisUCI]

Hi! It's a little hard to debug for me without seeing the data. I looked at a few similar examples from the Altair docs and they seemed to use a little different strategy:

• https://altair-viz.github.io/gallery/bump_chart.html
  uses x = alt.X("date:O", timeUnit="yearmonth")

• https://altair-viz.github.io/gallery/bar_rounded.html
  uses x='month(date):O'

I would also start without the axis and scale arguments, just so at first there are fewer parts making adjustments.

Does that help? If not, can you post an example of the behavior using one of the datasets from vega_datasets, like in the gallery examples?

[lucasbalponti]

Hi Cristopher,

Your first suggestion solved my problem ( x = alt.X("date:O", timeUnit="yearmonth") ):

Thank you for the precise and quick answer!

[lucasbalponti]

Update: i realized that after i made the change, the dates were off by one day.

But then i just transformed the dates to a string, formatted like ISO 8601, added my timezone info, and everything worked perfectly!

[joelostblom]

Closing as resolved. Some more info on the off-by-one dates in this issue #2540