title: Invert axis direction Altair
body: <p>For some reason, the Y-axis while plotting with altair seems to be inverted (would expect values to go from lower (bottom) to higher (top) of the plot). Also, I would like to be able to change the ticks frequency. With older versions I could use <code>ticks=n_ticks</code> but it seems now this argument can take only boolean.</p>
  <pre><code>import altair as alt
  alt.renderers.enable('notebook')
  
  eff_metals =  pd.read_excel(filename, sheet_name='summary_eff_metals')
  points = alt.Chart(eff_metals, height=250, width=400).mark_circle().encode(
      x=alt.X('Temperature:Q',axis=alt.Axis(title='Temperature (°C)'),
              scale=alt.Scale(zero=False, padding=50)),
      y=alt.Y('Efficiency:N',axis=alt.Axis(title='Efficiency (%)'),
              scale=alt.Scale(zero=False, padding=1)),
      color=alt.Color('Element:N'),
  )
  text = points.mark_text(align='right', dx=0, dy=-5).encode(
      text='Element:N'
  )
  chart = alt.layer(points, text, data=eff_metals, 
                    width=600, height=300)
  chart
  </code></pre>
  <p>And the figure:
  <a href="https://i.stack.imgur.com/urLTX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/urLTX.png" alt="enter image description here" /></a></p>