Use x and y parameters for Image trace in imshow (for RGB or binary_string=True)

[emmanuelle]

Closes #2758

I could only get it to work for numerical data types, I don't think the x0 and dx parameters of go.Image are meant to work with str or datetime types (could you please confirm @antoinerg?)

For example for the airtemps dataset used in the imshow tutorial, this now works

[nicolaskruchten]

What does the output look like if you try this with an xarray with dates?

[nicolaskruchten]

or should we raise in that case instead of trying to render?

[nicolaskruchten]

@emmanuelle bump on my last comment :)

[emmanuelle]

@nicolaskruchten looks like

(dates are converted to time intervals I guess)

I'll look into accepting only numerical types for x and y.

[nicolaskruchten]

thanks! I think the dates are just ignored and the axis just counts pixels actually... not all that graceful :(

[nicolaskruchten]

this is correct but I think a bit opaque for users? in the xarray case they've maybe not specified x (as it's implicit) and they don't know they're using an Image trace (all they know is they set binary_string=True

[emmanuelle]

ok I can think of a better error message, but do we agree that we should also error when x is passed explicitly and does not have a numerical dtype? (otherwise it would just be ignored, which I agree is not a good thing).

[emmanuelle]

I changed the error message, is it better now?

[nicolaskruchten]

LGTM! 💃