How to assign different colors for data in different rows from a dataframe?

For instance, here's a dataframe

T=[label X Y

A 1 2

A 4 5

B 3 5

B 9 10]

I want to make a scatter plot with Y against X, but assign different colors and shapes based on their labels (i.e, A and B). How can I accomplish that? Many thanks!

I can think of using T{1:2,2} to extract different rows, but the real data contain many rows and more than two labels, so it's difficult to count row by row

Answer 1

[Image Analyst]

Maybe something like untested

% letters = T{:, 1};
% x = T{:, 2};
% y = T{:, 3};
letters = {'A'; 'A'; 'B'; 'B'}

letters = 4×1 cell array
    {'A'}
    {'A'}
    {'B'}
    {'B'}

numUniqueLetters = length(unique(letters))

numUniqueLetters = 2

x = [1;4;3;9]

x = 4×1

1 4 3 9

y = [2; 5; 5; 10];
colors = jet(numUniqueLetters)

colors = 2×3

0 0 1 0 1 1

g = findgroups(letters)

g = 4×1

1 1 2 2

markerColors = colors(g, :)

markerColors = 4×3

0 0 1 0 0 1 0 1 1 0 1 1

scatter(x, y, 300, markerColors, 'filled')
grid on;

[Zhe Dong]

Thanks very much for your answer! it works good, is there a way that I can specify the colors instead of using the defult ones?

[Zhe Dong]

And seems in this way I can't assign different shapes to different labels?

[Image Analyst]

The colors are what you tell it to use. Like I did:

colors = jet(numUniqueLetters)

jet is one of many colormaps you can use. See the colormap and colorbar documentation for other built-in colormaps. Or you can make up your own N-by-3 matrix of custom colors.

To have different shapes, you'd need to call scatter() once per shape. So get a subset of x and y then call scatter for that subset. To get x and y for set #1:

x1 = x(g == 1);
y1 = y(g == 1);
scatter(x1, x2, 300, markerColors, 'filled', 'Marker', 'd') % Use diamond marker.

If that works, are you ready to "Accept this answer"?

[Zhe Dong]

In subset of x and y like your example, I can no longer use the 'markerColor' because of the lengh inconsistency, but I figured it out. Anyway, thanks!

[Image Analyst]

Well you'd do this

markerColors = colors(g == 1, :)

[Zhe Dong]

Hi sorry to bother you again, in the example you presented above, how can I add legends to different groups (i.e., different colored dots)? coz it seems that matlab sees these dots as the same group when I try to add legends, thanks in advance!

[Image Analyst]

You could call scatter several times with a different color each time, or you could use gscatter().

[Zhe Dong]

Thanks a lot, that helps!