在Python中绘图仅从CSV中提取特定列

Question

编辑：正如建议缩短问题：

python和编程的新手，我想将第1和第4列绘制成log（x）log（y）图。老实说，我不知道如何从中提取我需要的两列。

16:58:58 | 2.090 | 26.88  | 1.2945E-9  |   45.8
16:59:00 | 2.031 | 27.00  | 1.3526E-9  |  132.1
16:59:02 | 2.039 | 26.90  | 1.3843E-9  |  178.5
16:59:04 | 2.031 | 26.98  | 1.4628E-9  |  228.9
16:59:06 | 2.031 | 27.04  | 1.5263E-9  |  259.8
16:59:08 | 2.027 | 26.84  | 1.6010E-9  |  271.8

Answer 1

使用pandas：

import pandas as pd
df = pd.read_csv("data.txt", delimiter="\s[|]\s+", header=None, index_col=0)
df.plot(y=4)

（请注意，这会忽略对数缩放，因为它不清楚时间的对数应该是什么）

Answer 2

如果你不想使用优秀的pandas，这是一种蒸汽方法。

import matplotlib.pyplot as plt
import math
import datetime as dt

test = """16:58:58 | 2.090 | 26.88  | 1.2945E-9  |   45.8\n
16:59:00 | 2.031 | 27.00  | 1.3526E-9  |  132.1\n
16:59:02 | 2.039 | 26.90  | 1.3843E-9  |  178.5\n
16:59:04 | 2.031 | 26.98  | 1.4628E-9  |  228.9\n
16:59:06 | 2.031 | 27.04  | 1.5263E-9  |  259.8\n
16:59:08 | 2.027 | 26.84  | 1.6010E-9  |  271.8\n"""

lines = [line for line in test.splitlines() if line != ""]

# Here is the real code
subset = []

for line in lines:
    parts = line.split('|')
    ts = dt.datetime.strptime(parts[0].strip(), "%H:%M:%S")
    num = math.log(float(parts[3].strip()))
    subset.append((ts, num))

# now there is a list of tuples with your datapoints, looking like
# [(datetime.datetime(1900, 1, 1, 16, 58, 58), 1.2945E-9), (datetime.datetime(1900, 1, 1, 16, 59), ...]
# I made this list intentionally so that you can see how one can gather everything in a tidy way from the
# raw string data.

# Now lets separate things for plotting
times = [elem[0] for elem in subset]
values = [elem[1] for elem in subset]

# now to plot, I'm going to use the matplotlib plot_date function.
plt.figure()
plt.plot_date(times, values)
# do some formatting on the date axis
plt.gcf().autofmt_xdate()
plt.show()