Provide data to graphs beyond Float pairs

[KarthikRIyer]

Initial discussion regarding this can be found here:
#23 (comment)

[KarthikRIyer]

@BradLarson @marcrasi, as the first evaluation is coming up on 24th, is there anything specific I need to complete before that?
I am trying to change one plot to Generics and see how that works out. If that I am unable to get it working before the first evaluation maybe I can update the documentation for the work done till now.

[KarthikRIyer]

Now I am not sure if generics is the correct way to proceed.
I am unable to use operators like:

static func + (left: Point, right: Point) -> Point {
        return Point(left.x + right.x, left.y + right.y)
    }

Even if I write a protocol Addable overloading the + operator, it wont work because then I still wont be able to use other operations like * - / etc.
If I write protocols for each of these then I wont be able to use String.

Making the input for each plot conform to specific protocols seems like the right way. But is that not kind of what we are doing right now? We are accepting only specific data types. Maybe we can also have overload for Int, Double, etc...but we'll have to add extra variables for them in the Point type like I did for String...

How was this handled in CorePlot?

[marcrasi]

@BradLarson @marcrasi, as the first evaluation is coming up on 24th, is there anything specific I need to complete before that?

No, you've already done everything I'm looking for in the first milestone and you're doing really great in everything the evaluation asks about :)

[marcrasi]

about generics, I haven't thought much about how you could use them for plotting data types, but here's an initial answer to your question.

If you make Point generic over the x and y types like Point<X, Y> then you can define operations that only make sense for certain types of point like this:

extension Point where X: AdditiveArithmetic, Y: AdditiveArithmetic {
  static func + (left: Point, right: Point) -> Point {
    ...
  }
}

[KarthikRIyer]

Thanks! I didn't know that we could write such generic specific extensions. I'll try this and see if it helps.

[BradLarson]

@KarthikRIyer - On the matter of evaluations, as Marc said, you're doing great. You've hit the initial milestone objectives and gotten this to a demonstrable state both at the console and in Jupyter notebooks.

In fact, your work in using lodepng, setting up your Swift / C / C++ targets, and interacting with Jupyter was really informative to watch and helped me finally get my GPUImage framework operational once again on Linux and with Jupyter notebooks. Learning goes both ways on a project like this.

[KarthikRIyer]

@BradLarson glad that working together on this helped you too!
I'm hoping to complete all the milestones by the second evaluations, and then maybe I can work on supporting macOS and iOS.

[KarthikRIyer]

@BradLarson @marcrasi I don't think generics is a good because when I started by turning the Point type to a generic, I eventually realised that I had to convert all types to generics. Even the types like Series, Axis, etc. It's also becoming kind of difficult to handle different types. For example:
If I need to find the number of digits in 324.01, before, I converted it into Int which gave me 324 and I got the digits. Now I am using a generic T conforming to a protocol I wrote called NumericType. I am unable to convert it into an Int unless the generic conforms to BinaryInteger. I checked an existing plotting framework thinking it would help: https://github.com/danielgindi/Charts

This didn't help. They seem to have used Double everywhere and have different data input types for each plot, like LineChartDataEntry, PieChartDataEntry, BarChartDataEntry.
It's done in a similar manner in a popular android plotting framework: https://github.com/PhilJay/MPAndroidChart

I had faced the same issue when working on my previous plotting project Graph-Kit. I'd opted to use float then.

Can we use the same method we're using right now? Maybe use Double instead of Float?
How was this handled in CorePlot? I was trying to read the file CPTNumericDataType.m, but couldn't understand much.
Any ideas on how we can proceed?

[KarthikRIyer]

Till this is figured out I'll start work on histogram.

[KarthikRIyer]

Also could you give me an idea of how people would want to plot using Tensors?
I gave this a fleeting look: https://www.tensorflow.org/swift/tutorials/model_training_walkthrough
But in the end plotting is done using arrays

[BradLarson]

Sorry I've been away from this, have been busy with other matters. For types, I think it's worth approaching this from the standpoint of what is needed by the plot types and what people will want to provide as inputs.

For a scatter plot, for example, your plots will need a type on the X and Y axes that can be converted to a floating-point number so that display arithmetic can be done with it. For a bar chart, the Y axis will need to be floating-point convertible, but the X axis will need hashable values (for binning) that can be represented as a String. You need to somehow define the inputs (probably using protocols) to a plot, and then allow users to supply the various types of input data that can be converted to that.

You may not even need to use generics here, because I don't know that it's essential to preserve type information all the way through to your plot. We'd have to think about if type erasure would be acceptable.

I'm thinking that Point might not be the most expressive name here, given the different input types you might be dealing with. I could see renaming it to Pair<T, U> and possibly Triplet<T, U, V> for 2-D and 3-D plots, respectively. If type erasure wasn't a concern, you could then have scatter plots take in series of Pair<FloatConvertible, FloatConvertible> values, and bar charts could have Pair< CustomStringConvertible, FloatConvertible> values. Arithmetic and other operations could be done by first casting the FloatConvertible values to Float and working with them from there.

[BradLarson]

Also, is pairing off each datapoint going to work for all cases? In a scatter plot, I can see people wanting to provide two or more series of Y values that share the same series of X values. Is this approach generic enough to support that?

[KarthikRIyer]

I'll try working with the Pair<> approach.

Regarding the scatter plot, input is in given as an array for x and an array for y using the addSeries function....
So if we need the same x values and different y values we can just add another series passing in the same x array.