Difference chart - understand the x-position for city names

Community Help
1

Hello. Can someone explain me how x is found for the text mark without using ‘x:’?

Bonus point to explaining the use of …Plot.selectMinY(…) too :slight_smile:

Plot.text(data, {
  ...Plot.selectMinY({
    x: "date",
    y: "New York",
    text: () => "San Francisco"
  }),
  y: "San Francisco",
  dy: -40
})
2

x is defined on line 3. selectMinY will only consider the index of the data point that has the minimum temperature in New York (line 4), and will return both channels x and y (and also text, for that matter).

Then on line 7 we override the y channel by the temperature in San Francisco, so we end up with the x channel being all the dates, the y channel being all the temperatures in SF, and the index being the one that gives the minimum temperature in NYC.

3

Thank you for the explanation.

When reading it initially It felt that by having x embedded in the selectMinY it was not out of scope for the text mark.

In my head (i.e. wrong) I was expecting something like:
x:
…Plot.selectMinY({
x: “date”,
y: “New York”,
text: () => “San Francisco”
})