Matplotlib不绘制线条图;十字架，圆圈和三角形的工作

Question

我想用Matplotlib绘制一些测量数据。 用下面显示的代码，我得到了绘图窗口和GUI，但没有绘制任何绘图。如果我把这种情节改成圆形或十字形，它就可以正常工作。

# coding=utf-8 
import matplotlib.pyplot as plt 
import csv 

with open("AgPVP8.2.171g1L#2.csv") as csvfile: 
    reader = csv.reader(csvfile, delimiter=",") 

    frequencies = [] 
    phases = [] 

    for row in reader: 
     frequency = float(row[0]) 
     phase = float(row[4]) 

     frequencies.append(frequency) 
     phases.append(phase) 

plt.plot([frequencies], [phases], "b-") 
plt.xscale("log") 
plt.show() 

Answer 1

plt.plot(x,y)需要x和y为列表（或一般序列）或数组。 在这里，您尝试绘制一个列表的列表，即[x]与x不一样。 因此，在你的代码，你需要

plt.plot(frequencies, phases, "-b") 

更换plt.plot([frequencies], [phases], "b-")然后完整的代码应该是这样的：

import matplotlib.pyplot as plt 
import csv 

with open("AgPVP8.2.171g1L#2.csv") as csvfile: 
    reader = csv.reader(csvfile, delimiter=",") 

    frequencies = [] 
    phases = [] 

    for row in reader: 
     frequency = float(row[0]) 
     phase = float(row[4]) 

     frequencies.append(frequency) 
     phases.append(phase) 

plt.plot(frequencies, phases, "b-") 
plt.xscale("log") 
plt.show() 

我建议看看numpy.loadtxt或numpy.genfromtxt。这两种方式都会使得在csv文件中读取更容易，例如，在这种情况下

import matplotlib.pyplot as plt 
import numpy as np 

frequencies, phases = np.loadtxt("AgPVP8.2.171g1L#2.csv", unpack=True, usecols = (0,4), delimiter=",") 

plt.plot(frequencies, phases, "b-") 
plt.xscale("log") 
plt.show() 

Answer 2

的问题是，频率和相位仅在with open(...范围存在，则必须在该放置：

import matplotlib.pyplot as plt 
import csv 

with open("AgPVP8.2.171g1L#2.csv") as csvfile: 
    reader = csv.reader(csvfile, delimiter=",") 

    frequencies = [] 
    phases = [] 

    for row in reader: 
     frequency = float(row[0]) 
     phase = float(row[4]) 

     frequencies.append(frequency) 
     phases.append(phase) 
    plt.plot(frequencies, phases, "-b") 
    plt.xscale("log") 
    plt.show()