topic Re: Contour Plot with Gradient Colors in Graphics Programming

Contour Plot with Gradient Colors

NKormanik — Tue, 06 Aug 2019 10:47:47 GMT

I'm attempting to create a contour plot (proc gcontour) that uses a gradient of colors -- ideally, dark blue, through to, red. Dark blue would show the lowest of values. Red, the highest.

So far I can think only of listing all colors that I'd like to use, via goptions, colors=().

The colors would likely have to be in hexadecimal format (CXFF0000, etc.).

If I want to show 20 levels on the contour plot, I'd have to come up with a 20-member list in hexadecimal format. Somehow uniformly spaced throughout the range.

Would be really nice if SAS can automatically generate such a gradient for a contour plot.

Am I simply missing it?

Sure hope so.

Please advise.

Nicholas Kormanik

Re: Contour Plot with Gradient Colors

Rick_SAS — Tue, 06 Aug 2019 12:38:46 GMT

You can use the PALETTE function in SAS/IML to create custom color ramps.

- Documentation

- Examples and discussion

If you switch from PROC GCONTOUR and instead

define a contour plot by using the GTL template and the CONTOURPLOTPARM statement, then you can use the COLORMODEL= option to define a color ramp. You can use the syntax COLORMODEL=(blue red) to define a two-color ramp that linearly interpolates between blue and red. Or you can use the built-in COLORMODEL=ThreeColorRamp to use a three-color ramp that goes from blue (low) to white (neutral) to red (high).

Re: Contour Plot with Gradient Colors

NKormanik — Wed, 07 Aug 2019 04:36:20 GMT

Thank you, Rick. Really appreciate you being available here to help. As well as all the others. Amazing community.

Nicholas

Re: Contour Plot with Gradient Colors

NKormanik — Thu, 08 Aug 2019 10:01:45 GMT

Is there any way of continuing to use PROC GCONTOUR, and also use COLORMODEL=ThreeColorRamp?

That would be exactly what I am wanting to do.

If not, why not? Is Proc Gcontour being deprecated?

Re: Contour Plot with Gradient Colors

Rick_SAS — Thu, 08 Aug 2019 10:48:03 GMT

The COLORMODEL= option is supported in GTL and in the SG procedures, but not (as far as I know) in the GCONTOUR procedure. The GCONTOUR procedure uses a different syntax, which I am not very familiar with because I started learning SAS graphics when the SG (statistical graphics) procedures were being developed. I'll leave it to others to suggest ways to solve your problem by using PROC GCONTOUR.

Re: Contour Plot with Gradient Colors

DanH_sas — Thu, 08 Aug 2019 14:25:13 GMT

If you want to continue to use PROC GCONTOUR, but have gradient colors, I think you best option is to go to to the color brewer site, select the pallette and number of levels you want, and put those colors in your GOPTIONS COLORS= option. Here is the URL for the site: http://colorbrewer2.org/#type=sequential&scheme=BuGn&n=3

Hope this helps!
Dan

Re: Contour Plot with Gradient Colors

NKormanik — Fri, 09 Aug 2019 01:27:49 GMT

Terrific site, Dan. Will do that for now, just add colors in goptions.

But will have to learn the SG procedures as well, as Rick suggests.

Thanks for your help.

Re: Contour Plot with Gradient Colors

NKormanik — Fri, 09 Aug 2019 06:16:13 GMT

Beautiful....

Re: Contour Plot with Gradient Colors

DanH_sas — Fri, 09 Aug 2019 14:16:59 GMT

Just for completeness, I'll mention that the color list could also be specified on the CLEVELS option instead of the GOPTIONS COLORS= option. That way, the colors would not affect any other SAS/Graph plots or force you to do a GOPTIONS RESET=ALL before generating the next plot.

Thanks!
Dan

Re: Contour Plot with Gradient Colors

NKormanik — Sat, 10 Aug 2019 07:44:52 GMT

One more question....

I vaguely recollect that SAS holds somewhere -- at least temporarily -- nearly every aspect of the output of all procedures. Sort of hidden away. That if you want to extract/save any of this, it's possible. If you just know where exactly to find it.

So, in the contour plot above, at bottom, is the legend, specifying the contour levels.

I would like to save that data vector, in .sas7bdat, or in .txt, etc., format. And give the extracted/saved file a name -- i.e., "contour_levels_xyz.sas7bdat".

Any continuing help greatly appreciated.

Re: Contour Plot with Gradient Colors

Rick_SAS — Sat, 10 Aug 2019 12:39:24 GMT

You might be thinking about using ODS OUTPUT to save tables into data sets. You can also use ODS OUTPUT to output the data values on the ODS statistical graphics that are created from SAS procedures or from the SG procedures. That is one of the advantages to using ODS GRAPHICS: all output goes through ODS which means you can select it, store it, send it to various destinations, etc.

Re: Contour Plot with Gradient Colors

NKormanik — Sun, 11 Aug 2019 05:35:03 GMT

Thanks, Rick. Great lead.

Unfortunately in the present case only output is the original input data set. No sign at all of the vector of numbers used for the contour divisions.

Perhaps this is an additional reason to move on to SG, GTL, IML, whatever. Maybe one of these can produce a contour map with savable contour divisions.

If anyone wants to help get there.....

Re: Contour Plot with Gradient Colors

Rick_SAS — Sun, 11 Aug 2019 10:13:09 GMT

Do you know (or can you determine) the maximum and minimum value of the surface on the rectangular domain that you are plotting?

If so, you can determine the contour levels.

Contours are determined by evenly spaced subdivisions in the range of the Z value of the data. So if you want M contours then they are positions at

z = Zmin + k*dz, for k=1, 2, 3, ..., M

and dz = (ZMax = ZMin) / (M+1)

where ZMin = min(z on rectangular domain) and ZMax = max(z on rectangular domain).

For example, in your picture, it looks like

ZMin ~ -20.5

ZMax ~ 21.6

and you have M=18 contours so

dz = (21.6 - (-20.5) / 19= 2.216 and the contours are at the heights

z1 = -20.5 + 2.216;

z2 = -20.5 + 2* 2.216;

...

data Levels;
zMax = 21.6;   /* max of surface on rectangle */
zMin = -20.5;
M = 18;        /* number of contours */
dz = (zMax - zMin) / (M+1);
do i = 1 to M;
   z = zMin + i*dz;
   output;
end;
run;

proc print data=levels;
var i z;
run;

Re: Contour Plot with Gradient Colors

NKormanik — Mon, 12 Aug 2019 06:22:07 GMT

Beautifully shown, Rick. Good for my own understanding and reference, as well as useful for others. Thanks!

Do you know (or can you determine) the maximum and minimum value of the surface on the rectangular domain that you are plotting?

Well, I was hoping that the contour process itself would give me those values. I have hundreds of such data sets to examine. If I could have extracted contour vectors for each one, I was then hoping to cluster-analyze them. Without the data I will simply have to eyeball the graphs, to try to make sense somehow.

At any rate, I may have been overestimating the value of capturing those contour values. May be better to proceed on to other avenues.

The objective, though, is to study 3D representations of data sets. Will presently turn to proc loess, proc kde, proc krige2d, etc.

Of these, are you particularly keen on one versus another?

All comments welcome.

Re: Contour Plot with Gradient Colors

Rick_SAS — Mon, 12 Aug 2019 12:05:17 GMT

I have some experience with those procedures. They do different things:

1) LOESS assumes that Z (the response) is a nonparametric of (X, Y). Local weighted regression is used to predict Z.

2) KDE is quite different. It estimates the density of (X, Y). It does not predict a third variable, Z.

3) KRIGE2D is a spatial analysis procedure. You should use it only if your (X, Y) data represent coordinates (spatial locations) in some field or forest.

There are other procedures such as PROC GLMMIX and PROC GAMPL that can model responses by using parametric or nonparametric models.

Which procedure I would recommend depends on what you are trying to accomplish. I do not know what you mean by " 3D representations of data sets." Do you have a reference, or can you describe the business use for the analysis?

Re: Contour Plot with Gradient Colors

NKormanik — Tue, 13 Aug 2019 07:49:38 GMT

I've been trying to ascertain if there is any legitimacy to "stock trading, technical analysis."

As I see it, the main problem is all the 'noise.' Randomness going on. Inconsistency. No sure thing. But wondering if there exist some general tendencies.

I've collected the following data:

Y = price change over the next three days

X1 = a particular level of one 'technical indicator' today

X2 = a particular level of a second 'technical indicator' today

Data for some stock, over a number of years.

Please refer to the contour chart posted above several days ago.

Assuming someone is going to trade -- even given all the risks and randomness -- then it appears from the contour chart that the optimal time to trade is when:

X1 ("23403") is low.

X2 ("23401") is high.

This theoretically should be associated with Y ("50401") being high.

No certainty, of course. But at least one would be taking statistics into account.

A contour chart seems like it could be one approach to solving the problem. Hoping there are others, as well, such as Proc Loess, etc.

Re: Contour Plot with Gradient Colors

Rick_SAS — Tue, 13 Aug 2019 09:51:40 GMT

I see. You might want to overlay the data on the contour plot. If the explanatory variables are correlated (which they probably are), the corner of the plots (which you think are optimal) might be outside the range of the data. You might be looking at the extrapolated predictions. Models will have high prediction errors and can even predict nonsensical results when you evaluate the model outside the range of the data. See the article "Interpolation vs extrapolation: the convex hull of multivariate data"

Anyway, don't use kriging or any other spatial analysis procedure since you do not have spatial data. Good luck.

Re: Contour Plot with Gradient Colors

GraphGuy — Tue, 13 Aug 2019 13:46:28 GMT

Here's how to do it with Proc GContour, and let the ODS Style generate the color ramp for you ...

proc template;
define style styles.my_grad;
parent=styles.htmlblue;
style twocolorramp / startcolor=red endcolor=navy;
end;
run;

ods html style=my_grad;
proc gcontour data=sashelp.lake;
plot width*length=depth / nolegend pattern;
run;

Re: Contour Plot with Gradient Colors

NKormanik — Wed, 14 Aug 2019 08:10:25 GMT

Thanks, Robert. Great addition here.

And thanks again, Rick. Your suggestions are always so clear. Terrific.

Re: Contour Plot with Gradient Colors

NKormanik — Tue, 20 Aug 2019 07:01:10 GMT

Below is a contour/gradient chart produced by Proc LOESS, using the same data as above:

Notice how it differs greatly from the contour chart from Proc GCONTOUR (way above).

The difference seems primarily due to two Proc LOESS model parameters:

degree = 2
interp=cubic

Clueless as to what to use, frankly.

Other SAS procedures that appear to hold promise in producing a fitting contour/gradient representation are:

Proc GAM

Proc GAMPL

Researching at present how to use these. Are they even appropriate.

Objective, once again: X1, X2 ---> Y. Graphically. Contour. Gradient.

Any leads greatly appreciated.

Nicholas