python/matplotlib - multicolor line

Question

I am trying to create a colored line with certain conditions. Basically I would like to have the line colored red when pointing down on the y axis, green when pointing up and blue when neither.

I played around with some similar examples I found but I have never been able to convert them to work with plot() on an axis. Just wondering how this could be done.

Here is some code that I have come up with so far:

CREATE TABLE `sessions` (
`id` int(128) NOT NULL AUTO_INCREMENT,
`ip` varchar(128) COLLATE latin1_general_ci NOT NULL,
`hostname` varchar(128) COLLATE latin1_general_ci NOT NULL,
`city` varchar(128) COLLATE latin1_general_ci NOT NULL,
`region` varchar(128) COLLATE latin1_general_ci NOT NULL,
`country` varchar(128) COLLATE latin1_general_ci NOT NULL,
`loc` varchar(128) COLLATE latin1_general_ci NOT NULL,
`org` varchar(128) COLLATE latin1_general_ci NOT NULL,
`postal` varchar(128) COLLATE latin1_general_ci NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci     AUTO_INCREMENT=1 ;

Not sure how to get plot() to accept an array of colors. I always get an error about the format type used as the color. Tried heximal, decimal, string and float. Works perfect with scatter().

Thanks

Answer 1

我认为你不能在plot中使用颜色数组（文档说颜色可以是任何matlab颜色，而scatter文档说你可以使用数组）。

但是，你可以通过分别绘制每一行来伪造它：

import numpy
from matplotlib import pyplot as plt

x = range(10)
y = numpy.random.choice(10,10)
for x1, x2, y1,y2 in zip(x, x[1:], y, y[1:]):
    if y1 > y2:
        plt.plot([x1, x2], [y1, y2], 'r')
    elif y1 < y2:
        plt.plot([x1, x2], [y1, y2], 'g')
    else:
        plt.plot([x1, x2], [y1, y2], 'b')

plt.show()

Answer 2

行。所以我想出了如何使用LineCollecion在轴上绘制线条。

import numpy as np
import pylab as pl
from matplotlib import collections  as mc

segments = []
colors = np.zeros(shape=(10,4))
x = range(10)
y = np.random.choice(10,10)
i = 0

for x1, x2, y1,y2 in zip(x, x[1:], y, y[1:]):
    if y1 > y2:
        colors[i] = tuple([1,0,0,1])
    elif y1 < y2:
        colors[i] = tuple([0,1,0,1])
    else:
        colors[i] = tuple([0,0,1,1])
    segments.append([(x1, y1), (x2, y2)])
    i += 1     

lc = mc.LineCollection(segments, colors=colors, linewidths=2)
fig, ax = pl.subplots()
ax.add_collection(lc)
ax.autoscale()
ax.margins(0.1)
pl.show()

Answer 3

有example on the matplotlib page显示如何使用LineCollection绘制多色线条。

剩下的问题是获取行集合的颜色。因此，如果y是要比较的值，

cm = dict(zip(range(-1,2,1),list("gbr")))
colors = list( map( cm.get , np.sign(np.diff(y))  ))

完整代码：

import numpy as np; np.random.seed(5)
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection

x = np.arange(10)
y = np.random.choice(10,10)

points = np.array([x, y]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)

cm = dict(zip(range(-1,2,1),list("rbg")))
colors = list( map( cm.get , np.sign(np.diff(y))  ))

lc = LineCollection(segments, colors=colors, linewidths=2)
fig, ax = plt.subplots()
ax.add_collection(lc)

ax.autoscale()
ax.margins(0.1)
plt.show()