2D scatter with colormap effective on both axes - Python

Question

I have been reading a lot of similar posts like here, here, here, and so on, yet I am not able to fix my problem. I need the colormap for my scatter plot to be effective on both axes, yet it can work on one axis only (in my example, axis "x"):

my_list = [[73, 84], [69, 84], [66, 84], [76, 83], [73, 83], [62, 84], [62, 83], [73, 79], [61, 84], [61, 83], [60, 90], [62, 79], [58, 84], [57, 90], [61, 79], [60, 79], [57, 84], [58, 83], [55, 84], [59, 79], [57, 83], [58, 79], [50, 84], [55, 83], [48, 84], [57, 79], [47, 84], [55, 79], [46, 93], [73, 78], [46, 84], [50, 83], [54, 79], [61, 78], [45, 88], [50, 79], [45, 84], [58, 78], [47, 83], [48, 79], [57, 78], [62, 20], [44, 84], [46, 83], [47, 79], [55, 78], [60, 20], [43, 84], [44, 83], [41, 84], [58, 20], [46, 79], [55, 25], [70, 15], [38, 95], [43, 83], [40, 84], [38, 89], [57, 20], [44, 79], [55, 24], [65, 15], [34, 100], [55, 20], [62, 19], [43, 79], [38, 84], [54, 24], [50, 78], [34, 95], [65, 13], [41, 83], [62, 13], [37, 84], [42, 79], [60, 19], [54, 20], [51, 24], [49, 78], [65, 10], [34, 90], [41, 79], [35, 84], [40, 83], [60, 15], [57, 19], [45, 78], [51, 20], [34, 88], [62, 10], [54, 19], [57, 15], [40, 79], [44, 78], [50, 20], [60, 10], [34, 84], [51, 19], [39, 79], [57, 10], [49, 20], [43, 78], [65, 8], [33, 84], [31, 88], [35, 83], [32, 84], [36, 79], [52, 15], [41, 78], [55, 10], [49, 19], [46, 74], [62, 8], [30, 90], [31, 84], [33, 83], [35, 79], [38, 78], [54, 10], [49, 15], [44, 74], [30, 88], [60, 8], [47, 19], [30, 84], [31, 83], [46, 20], [48, 15], [33, 79], [51, 10], [37, 78], [43, 25], [58, 8], [29, 90], [46, 19], [30, 83], [45, 20], [31, 79], [47, 15], [34, 78], [50, 10], [43, 24], [41, 74], [29, 84], [57, 8], [30, 79], [31, 78], [46, 15], [49, 10], [43, 20], [38, 24], [37, 74], [54, 8], [29, 83], [29, 79], [26, 84], [39, 20], [48, 10], [43, 15], [30, 78], [37, 24], [51, 8], [25, 90], [26, 83], [45, 10], [29, 78], [42, 15], [34, 74], [37, 20], [50, 8], [25, 84], [43, 13], [26, 79], [42, 14], [40, 15], [39, 19], [35, 20], [44, 10], [27, 78], [34, 24], [25, 83], [49, 8], [35, 19], [25, 79], [26, 78], [37, 15], [40, 13], [43, 10], [34, 20], [30, 74], [22, 84], [47, 8], [23, 79], [22, 83], [25, 78], [35, 15], [39, 10], [34, 19], [29, 74], [46, 8], [19, 90], [23, 78], [34, 15], [22, 79], [37, 10], [45, 8], [33, 20], [26, 74], [54, 5], [19, 88], [20, 79], [33, 19], [34, 14], [30, 20], [36, 10], [44, 8], [22, 78], [26, 25], [51, 5], [19, 84], [34, 13], [19, 79], [18, 84], [29, 20], [30, 19], [33, 15], [20, 78], [35, 10], [43, 8], [26, 24], [25, 74], [17, 88], [49, 5], [29, 19], [18, 79], [26, 20], [30, 15], [34, 10], [39, 8], [19, 78], [23, 24], [48, 5], [15, 88], [34, 9], [33, 10], [30, 14], [26, 15], [35, 8], [18, 78], [23, 20], [22, 74], [15, 84], [43, 5], [15, 83], [17, 78], [34, 8], [31, 10], [26, 14], [19, 74], [22, 20], [14, 84], [39, 5], [15, 79], [16, 78], [29, 10], [31, 8], [26, 13], [18, 74], [21, 20], [38, 5], [14, 83], [15, 78], [21, 19], [14, 79], [23, 15], [30, 8], [26, 10], [16, 74], [19, 20], [33, 5], [11, 84], [26, 9], [12, 79], [14, 78], [25, 10], [27, 8], [22, 15], [15, 74], [19, 19], [31, 5], [11, 83], [18, 19], [12, 78], [25, 8], [23, 10], [19, 15], [22, 14], [17, 20], [14, 74], [26, 5], [11, 79], [18, 15], [23, 9], [22, 10], [19, 14], [17, 19], [12, 74], [25, 5], [11, 78], [18, 14], [19, 10], [22, 9], [17, 15], [23, 5], [14, 20], [11, 74], [43, 3], [18, 10], [20, 9], [17, 14], [14, 19], [22, 5], [11, 24], [31, 3], [18, 8], [15, 14], [17, 10], [14, 15], [19, 5], [25, 3], [11, 20], [26, 0], [10, 78], [13, 15], [15, 10], [22, 3], [17, 5], [11, 19], [10, 74], [7, 84], [23, 0], [15, 8], [14, 10], [16, 5], [20, 3], [8, 74], [11, 15], [7, 78], [22, 0], [15, 5], [14, 8], [17, 3], [11, 13], [10, 20], [7, 74], [20, 0], [4, 79], [10, 15], [11, 10], [16, 3], [14, 5], [5, 78], [7, 20], [3, 88], [19, 0], [10, 14], [9, 15], [11, 9], [14, 3], [4, 78], [7, 19], [3, 79], [17, 0], [12, 5], [11, 8], [13, 3], [10, 10], [4, 74], [7, 15], [3, 78], [15, 0], [12, 3], [11, 5], [9, 10], [7, 14], [14, 0], [3, 20], [11, 3], [10, 5], [9, 9], [7, 10], [3, 19], [12, 0], [5, 10], [9, 5], [3, 15], [11, 0], [3, 14], [9, 3], [4, 10], [2, 19], [0, 84], [10, 0], [3, 10], [7, 8], [1, 78], [2, 14], [0, 79], [9, 0], [1, 74], [2, 10], [7, 0], [0, 78], [4, 5], [1, 10], [0, 74], [5, 0], [1, 8], [3, 5], [4, 0], [0, 10], [2, 3], [3, 0], [0, 8], [1, 3], [2, 0], [0, 5], [1, 0], [0, 3], [0, 0]]

x = [x[0] for x in my_list]
y = [x[1] for x in my_list]

plt.scatter(x, y, c=x, cmap='RdYlBu')
plt.colorbar()

As you see, the color map is working on "x" axis only. Now if I change my axis to "y", then this is what I would get:

What I need is a combination of these two .. that the color changes from red to blue from 0 to 100 on both axes. I have tried different ways and even different plots like imshow or heatmap, but scatter is what I need and I keep getting different errors. Could anyone help me to fix this please?

Could you explain what exactly you are trying to achieve? How would you like the plot to look like based on your input data? — ImportanceOfBeingErnest, Jun 10 '19 at 18:56
I think you need to be more explicit. For instance, how would you color (0, 40) vs (40, 0)? One approach is to use distance from origin as your metric for color coding data points. Not sure if that's your intention. — busybear, Jun 10 '19 at 18:58
@ImportanceOfBeingErnest You see how the color on "x" axis is changing from red to blue from left to right .. I want this to happen on "y" axis too and the color change from red to blue, from bottom to top. Like consider x = 0 .. the color is all red on "y" axis. I want it to change form red to blue .. like a 2D colormap. — RezAm, Jun 10 '19 at 18:59
@busybear I edited my question so hopefully it is more clear now. — RezAm, Jun 10 '19 at 19:03
@Antonio Do you mean you want it to colour diagonally like the image in [this post](https://stackoverflow.com/questions/17201172/a-logarithmic-colorbar-in-matplotlib-scatter-plot)? It's still not *entirely* clear — Nick is tired, Jun 10 '19 at 19:06
@NickA yessss .. exactly. Sorry I could not explain it more clearly! — RezAm, Jun 10 '19 at 19:08

score 1 · Accepted Answer · answered Jun 10 '19 at 19:12

To color code based on both x and y values, one method is to use their vector sum (or distance from origin). First, you define the distance for each point. Then use that distance for color coding:

import numpy as np

d = [np.sqrt(i**2 + j**2) for i, j in zip(x, y)]
plt.scatter(x, y, c=d, cmap='RdYlBu')
plt.colorbar()

2D scatter with colormap effective on both axes - Python

1 Answers1