Python从csv中删除负数条目/行

Question

我有一个不断增长的csv文件,看起来像:

143100, 2012-05-21 09:52:54.165852
125820, 2012-05-21 09:53:54.666780
109260, 2012-05-21 09:54:55.144712
116340, 2012-05-21 09:55:55.642197
125640, 2012-05-21 09:56:56.094999
122820, 2012-05-21 09:57:56.546567
124770, 2012-05-21 09:58:57.046050
103830, 2012-05-21 09:59:57.497299
114120, 2012-05-21 10:00:58.000978
-31549410, 2012-05-21 10:01:58.063470
90390, 2012-05-21 10:02:58.108794
81690, 2012-05-21 10:03:58.161329
80940, 2012-05-21 10:04:58.227664
102180, 2012-05-21 10:05:58.289882
99750, 2012-05-21 10:06:58.322063
87000, 2012-05-21 10:07:58.391256
92160, 2012-05-21 10:08:58.442438
80130, 2012-05-21 10:09:58.506494

当生成文件的服务具有API连接失败时,会出现负数.我已经使用matplotlib来绘制数据图形,但是人工负数会大大地压缩图形.我想找到所有否定条目并删除相应的行.在任何情况下,负数实际上都不代表任何实际数据.

在Bash我会做类似的事情:

awk '{print $1}' original.csv | sed '/-/d' > new.csv

但是这很麻烦而且往往很慢,如果我能帮助它,我真的不想在我的python图形脚本中嵌入bash命令.

谁能指出我正确的方向？

编辑:

这是我用来读取/绘制数据的代码:

import matplotlib
matplotlib.use('Agg')                                          
from matplotlib.mlab import csv2rec                           
import matplotlib.pyplot as plt                               
import matplotlib.dates as mdates                              
from pylab import *                                         

output_image_name='tpm.png'                   

data = csv2rec('counter.log', names=['packets', 'time'])   
rcParams['figure.figsize'] = 10, 5                              
rcParams['font.size'] = 8                                       

fig = plt.figure()                                              

plt.plot(data['packets'], data['time'])                      

ax = fig.add_subplot(111)                                       
ax.plot(data['time'], data['tweets'])                         
hours = mdates.HourLocator()                                    
fmt = mdates.DateFormatter('%D - %H:%M')                       
ax.xaxis.set_major_locator(hours)                               
ax.xaxis.set_major_formatter(fmt)                               

ax.grid()                                                

plt.ylabel("packets")                                         
plt.title("Packet Log: Packets Per Minute")         

fig.autofmt_xdate(bottom=0.2, rotation=90, ha='left')         

plt.savefig(output_image_name)

Answer 1

Python习惯用法是使用生成器表达式来过滤行:

sys.stdout.writelines(line for line in sys.stdin if not line.startswith('-'))

或者在处理环境中:

filtered = (line for line in sys.stdin if not line.startswith('-'))
for line in filtered:
    # ...