使用Python+Anaconda3读取CSV绘制3D颜色图报错求助

问题背景 #

近期在Anaconda3环境编写Python代码，目标是从CSV文件绘制3D颜色图，但被数据读取相关错误困扰多日。

原始代码 #

import numpy as np

import matplotlib.pyplot as plt

from mpl_toolkits.mplot3d import Axes3D

DataX_Y_1D = np.loadtxt("datacsv_1d_xy.csv", delimiter=",")

X, Y = np.meshgrid(DataX_Y_1D[:,0], DataX_Y_1D[:,1])

Z = np.loadtxt("datacsv_2d_Z.csv", delimiter=",")

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

ax.plot_surface(X, Y, Z)

plt.show()

遇到的错误 #

File "/Users/lenguyen/Desktop/test_3D/plot_3D_4.py", line 1, in <module>
    DataAll1D = np.loadtxt("datacsv_1d.csv", delimiter=",")
NameError: name 'np' is not defined

(base) lenguyen@ntmle2 test_3D % python plot_3D_4.py
Traceback (most recent call last):
  File "/Users/lenguyen/Desktop/test_3D/plot_3D_4.py", line 5, in <module>
    DataAll1D = np.loadtxt("datacsv_1d.csv", delimiter=",")
  File "/opt/anaconda3/lib/python3.9/site-packages/numpy/lib/npyio.py", line 1148, in loadtxt
    for x in read_data(_loadtxt_chunksize):
  File "/opt/anaconda3/lib/python3.9/site-packages/numpy/lib/npyio.py", line 999, in read_data
    items = [conv(val) for (conv, val) in zip(converters, vals)]
  File "/opt/anaconda3/lib/python3.9/site-packages/numpy/lib/npyio.py", line 999, in <listcomp>
    items = [conv(val) for (conv, val) in zip(converters, vals)]
  File "/opt/anaconda3/lib/python3.9/site-packages/numpy/lib/npyio.py", line 736, in floatconv
    return float(x)
ValueError: could not convert string to float: '\ufeff9.9'

错误分析 #

1. NameError: 出现name 'np' is not defined是因为某次运行的代码中遗漏了import numpy as np语句，你提供的代码里包含这行，应该是测试时的疏忽。
2. ValueError: 核心错误是\ufeff字符导致无法转成浮点数，这个字符是UTF-8 BOM（字节顺序标记），说明你的CSV文件是带BOM的UTF-8格式，而numpy默认的loadtxt不支持这种格式。

解决方案 #

方法1：修改numpy读取参数 #

在np.loadtxt中添加encoding='utf-8-sig'参数，让numpy识别带BOM的UTF-8文件。

方法2：修改CSV文件格式 #

用文本编辑器（如VS Code、Notepad++）打开CSV文件，重新保存为不带BOM的UTF-8格式（VS Code保存时选择"UTF-8"而非"UTF-8 with BOM"）。

额外注意 #

确保Z数组的形状和X、Y一致，meshgrid生成的X、Y是二维数组，所以Z也必须是相同尺寸的二维数组，否则plot_surface会报错。

修正后的代码 #

import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

# 读取带BOM的CSV文件，指定编码
DataX_Y_1D = np.loadtxt("datacsv_1d_xy.csv", delimiter=",", encoding='utf-8-sig')
X, Y = np.meshgrid(DataX_Y_1D[:,0], DataX_Y_1D[:,1])

# Z文件若同样带BOM，也添加encoding参数
Z = np.loadtxt("datacsv_2d_Z.csv", delimiter=",", encoding='utf-8-sig')

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')

ax.plot_surface(X, Y, Z)

plt.show()

内容的提问来源于stack exchange，提问作者EL-san