如何在散点图中绘制线条

Question

我无法相信这是如此复杂,但我现在尝试和谷歌搜索了一段时间.

我只是想用一些图形功能来分析我的散点图.对于初学者,我想简单地添加一行.

所以,我有几(4)分,我想给它添加一条线,就像在这个情节中一样(来源:http://en.wikipedia.org/wiki/File:ROC_space-2.png)

现在,这不起作用.坦率地说,文档-examples-gallery组合和matplotlib的内容是一个糟糕的信息来源.

我的代码基于图库中的简单散点图:

# definitions for the axes
left, width = 0.1, 0.85 #0.65
bottom, height = 0.1, 0.85 #0.65
bottom_h = left_h = left+width+0.02

rect_scatter = [left, bottom, width, height]

# start with a rectangular Figure
fig = plt.figure(1, figsize=(8,8))
axScatter = plt.axes(rect_scatter)

# the scatter plot:
p1 = axScatter.scatter(x[0], y[0], c='blue', s = 70)
p2 = axScatter.scatter(x[1], y[1], c='green', s = 70)
p3 = axScatter.scatter(x[2], y[2], c='red', s = 70)
p4 = axScatter.scatter(x[3], y[3], c='yellow', s = 70)
p5 = axScatter.plot([1,2,3], "r--")

plt.legend([p1, p2, p3, p4, p5], [names[0], names[1], names[2], names[3], "Random guess"], loc = 2)

# now determine nice limits by hand:
binwidth = 0.25
xymax = np.max( [np.max(np.fabs(x)), np.max(np.fabs(y))] )
lim = ( int(xymax/binwidth) + 1) * binwidth

axScatter.set_xlim( (-lim, lim) )
axScatter.set_ylim( (-lim, lim) )

xText = axScatter.set_xlabel('FPR / Specificity')
yText = axScatter.set_ylabel('TPR / Sensitivity')

bins = np.arange(-lim, lim + binwidth, binwidth)
plt.show()

一切都有效,除了p5是一条线.

现在该如何运作？这里有什么好的做法？

Answer 1

plot获取y值并使用x作为索引数组0..N-1或x和y值,如文档中所述.所以你可以使用

p5 = axScatter.plot((0, 1), "r--")

在你的代码中绘制线条.

但是,你要求"良好做法".以下代码(希望如此)显示了一些"良好实践"以及matplotlib的一些功能来创建您在问题中提到的情节.

import numpy as np
import matplotlib.pyplot as plt 

# create some data
xy = np.random.rand(4, 2)
xy_line = (0, 1)

# set up figure and ax
fig, ax = plt.subplots(figsize=(8,8))

# create the scatter plots
ax.scatter(xy[:, 0], xy[:, 1], c='blue')
for point, name in zip(xy, 'ABCD'):
    ax.annotate(name, xy=point, xytext=(0, -10), textcoords='offset points',
                color='blue', ha='center', va='center')
ax.scatter([0], [1], c='black', s=60)
ax.annotate('Perfect Classification', xy=(0, 1), xytext=(0.1, 0.9),
            arrowprops=dict(arrowstyle='->'))

# create the line
ax.plot(xy_line, 'r--', label='Random guess')
ax.annotate('Better', xy=(0.3, 0.3), xytext=(0.2, 0.4),
            arrowprops=dict(arrowstyle='<-'), ha='center', va='center')
ax.annotate('Worse', xy=(0.3, 0.3), xytext=(0.4, 0.2),
            arrowprops=dict(arrowstyle='<-'), ha='center', va='center')
# add labels, legend and make it nicer
ax.set_xlabel('FPR or (1 - specificity)')
ax.set_ylabel('TPR or sensitivity')
ax.set_title('ROC Space')
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)
ax.legend()
plt.tight_layout()
plt.savefig('scatter_line.png', dpi=80)

顺便说一句:我认为matplotlibs文档现在非常有用.