Altair: Move x-axis to y-axis zero.

[robertodr]

First of all, thanks for this fantastic library! I've only recently started using it and I like it much more than other tools I've used so far.

In the Line Chart with Points example, is it possible to move the x-axis to the zero of the y-axis? And if yes, how? I've searched in the docs, but I can't find any hints. Thanks in advance!

[Alcampopiano]

Hi there,

Are asking how to adjust the axis limits?

If so, would this work for you?

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

x = np.arange(100)
source = pd.DataFrame({
  'x': x,
  'f(x)': np.sin(x / 5)
})

alt.Chart(source).mark_line(point=True, clip=True).encode(
    x='x',
    y=alt.Y('f(x)', scale=alt.Scale(domain=[0, 1]))
)

If this is what you are looking for, you can find more information here in the docs

[robertodr]

Not quite. I want to keep the y < 0 plot (grid, line, points), but have the x axis in the position your plot shows.

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

x = np.arange(100)
source = pd.DataFrame({
  'x': x,
  'f(x)': np.sin(x / 5)
})

line = alt.Chart().mark_line(point=True).encode(
    x='x',
    y='f(x)', #alt.Y('f(x)', scale=alt.Scale(domain=[0, 1]))
)

hline = alt.Chart().mark_rule().encode(y='a:Q')

alt.layer(line, hline, data=source).transform_calculate(a="0")

This one gets the a line there, but the actual x axis stays at the bottom.

[Alcampopiano]

Hmm, good question. You could try something like this:

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

x = np.arange(100)
source = pd.DataFrame({
  'x': x,
  'f(x)': np.sin(x / 5)
})

alt.Chart(source).mark_line(point=True).encode(
    x='x',
    y='f(x)'
).configure_axisX(labelPadding=-150)

Perhaps there is something else that might help in the axis config section of the docs

[jakevdp]

A better way of doing this is with the axis offset property:

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

x = np.arange(100)
source = pd.DataFrame({
  'x': x,
  'f(x)': np.sin(x / 5)
})

alt.Chart(source).mark_line(point=True).encode(
    x=alt.X('x', axis=alt.Axis(offset=-150)),
    y='f(x)'
)

[robertodr]

Fantastic, thanks! Closing.