Z-zag time series plots

[elksie5000]

I'm not sure this is a bug report but I often seem to have what I call a zig-zag plot while trying plot time series

Probably best described with a question on Stackoverflow - the question

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Please follow these steps to make it more efficient to solve your issue:

• Since Altair is a Python wrapper around the Vega-Lite visualization grammar, most bugs should be reported directly to Vega-Lite. You can click the Action Button of your Altair chart and "Open in Vega Editor" to create a reproducible Vega-Lite example and see if you get the same error in the Vega Editor.
• Search for duplicate issues.
• Use the latest version of Altair.
• Describe how to reproduce the bug and include the full code and data to reproduce it, ideally using a sample data set from vega_datasets.

[ChristopherDavisUCI]

Thanks for the post. Can you please include a minimal example (including the portion defining the data)?

[elksie5000]

https://stackoverflow.com/questions/77213646/how-to-solve-unusual-time-series-plots-in-altair

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On Mon, 2 Oct 2023 at 14:05, Christopher Davis ***@***.***> wrote: Thanks for the post. Can you please include a minimal example (including the portion defining the data)? — Reply to this email directly, view it on GitHub <#3212 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAGZLVHOFVKCLXLM4PMSRNLX5K3ZFAVCNFSM6AAAAAA5O7V252VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTONBSHE3TSMRUGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[ChristopherDavisUCI]

Your Altair code looks fine to me, so my best guess is that it is an issue with the data. Maybe something with missing values? I tried using your sample data and was not able to reproduce the issue. (Is df a pandas DataFrame?)

[elksie5000]

Good morning, I hope you're well. I'm enjoying Voltaire and seeing what I can do with iit. Here's another example of odd plots. Not sure why. There is another quirk with a chart that I've attached on obesity-related hospital admissions. Sometimes you get that and when the chart loads, the area defaults to North East. However, if you click to another area and then click back it shows the right results. [image: image.png] This came from finding data that that the number of these admissions have risen from 300,000 in 2013 to 700,000 in 2019 (see top left). The second chart shows that around 2/3 of women are likely to be admitted than men and then I have a regional breakdown on the right. They are all really quite straightforward and Altair makes it easy to say switch the gender chart to the pie chart that has a hole in it. [image: image.png] I have one question about what is supposed to be the big visual for the data geeks (It is an attached in HTML). Some of the regions have a lot of local authorities and that means can difficult to see trends. How do do you make every line grey and bring it it up as red if you cross it or at least one of the points? I've seen it done but for the life of me can't get it to work. A simple workaround is to increase the sizes of the circles, I guess, but I don't know how to write the condition to highlight a line as red. And I'm guessing this is beyond the scope of the project, but would it be possible to create a feature to build on the back of the | and & functionality which would allow the creation of a simple HTML text box (Chart). I did try looking at the HTML of this project but suspect I'd break it if I tried to work it out myself. Anyway, thank you for keeping the project going. The hardest part of my project was cleaning the data, rather than creating largely through Altair. Kind regards. David Elks

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On Mon, 2 Oct 2023 at 14:05, Christopher Davis ***@***.***> wrote: Thanks for the post. Can you please include a minimal example (including the portion defining the data)? — Reply to this email directly, view it on GitHub <#3212 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAGZLVHOFVKCLXLM4PMSRNLX5K3ZFAVCNFSM6AAAAAA5O7V252VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTONBSHE3TSMRUGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[mattijn]

I'm loving the homophone of Voltaire to Altair!
Your last comment is not entirely visible on Github, this is what we see: #3212 (comment).

Regarding your original question in SO:
To use a temporal datatype you will have to cast your integer year column to strings in your DataFrame before pushing it into the Altair chart.

df = pd.DataFrame(
    {
        "year": [2014, 2015, 2016, 2017, 2018, 2019],
        "admissions": [200, 300, 450, 500, 700, 900],
    }
)
df.year = df.year.astype(str)  # <---

alt.Chart(df).mark_line().encode(alt.X("year:T"), alt.Y("admissions:Q"))

See also

• First issue with the request to have better support for integer years: Better deal with year integer? #1365
• This issue with the request to document this using string casting: Add an example of reading in years in a convenient manner #3162
• Apparently this is not necessary with VegaFusion activated: VegaFusion treats pandas categoricals differently than Altair's default transformer vegafusion#402 (comment)

I think this issue is resolved. Closing this issue for now.
Feel free to open a new issue for feature requests or if you see behavior that is potentially a bug.