如何在顯示時間時減少xticks標籤分辨率

Question

我的x軸上的標籤顯示一天的時鐘時間。每當我放大圖，他們看起來很傻，小數點後6位都是0。我毫不感興趣地顯示微秒。

見xticks標籤，在縮放前：

在放大後：

這是我今天：

ax_average.xaxis_date() 
fig_average.autofmt_xdate() 
fig_average.tight_layout() 

我怎樣才能確保只有幾秒鐘（或更好的分鐘）顯示在滴答標籤？

---

下面是代碼的稍微簡化版本繪出以上：

# Requires python-matplotlib 
import numpy 
from pylab import * 

raw_data = [ 
'Apr 20 12:14:36 a b temp_0 = 21.400000', 
'Apr 20 12:14:36 a b temp_1 = 17.860000', 
'Apr 20 12:14:36 a b temp_3 = 50.350006', 
'Apr 20 12:14:51 a b temp_0 = 21.400000', 
'Apr 20 12:14:51 a b temp_1 = 17.860000', 
'Apr 20 12:14:51 a b temp_3 = 50.350006', 
'Apr 20 12:15:06 a b temp_0 = 21.400000', 
'Apr 20 12:15:06 a b temp_1 = 17.860000', 
'Apr 20 12:15:06 a b temp_3 = 50.250000', 
'Apr 20 12:15:21 a b temp_0 = 21.400000', 
'Apr 20 12:15:21 a b temp_1 = 17.860000', 
'Apr 20 12:15:21 a b temp_3 = 50.250000'] 

def month_string_to_int(input): 
    if (input == 'Jan'): 
     return 1 
    elif (input == 'Feb'): 
     return 2 
    elif (input == 'Mar'): 
     return 3 
    elif (input == 'Apr'): 
     return 4 
    elif (input == 'May'): 
     return 5 
    elif (input == 'Jun'): 
     return 6 
    elif (input == 'Jul'): 
     return 7 
    elif (input == 'Aug'): 
     return 8 
    elif (input == 'Sep'): 
     return 9 
    elif (input == 'Oct'): 
     return 10 
    elif (input == 'Nov'): 
     return 11 
    elif (input == 'Dev'): 
     return 12 
    else: 
     print "Error in the month string: %s" % input 
     return -1 

data = {} 
timestamps = {} 
for line in raw_data: 
    line = line.strip() # strip newline character 
    lst = line.split() # space as separator 

    day = datetime.date(2015, month_string_to_int(lst[0]), int(lst[1])) 
    time = datetime.datetime.strptime(lst[2], "%H:%M:%S").time() 
    timestamp = datetime.datetime.combine(day, time) 

    identifier = lst[5] 
    value = float(lst[7]) 

    if identifier not in data: 
     data[identifier] = [] 
     timestamps[identifier] = [] 

    data[identifier].append(value) 
    timestamps[identifier].append(timestamp) 

fig, ax = subplots() 
plot(timestamps['temp_0'], data['temp_0']) 

ax.xaxis_date() 
fig.autofmt_xdate() 
fig.tight_layout() 

show() 

的timestamps字典看起來如我所料：

In [103]: timestamps 
Out[103]: 
{'temp_0': [datetime.datetime(2015, 4, 20, 12, 14, 36), 
    datetime.datetime(2015, 4, 20, 12, 14, 51), 
    datetime.datetime(2015, 4, 20, 12, 15, 6), 
    datetime.datetime(2015, 4, 20, 12, 15, 21)], 
'temp_1': [datetime.datetime(2015, 4, 20, 12, 14, 36), 
    datetime.datetime(2015, 4, 20, 12, 14, 51), 
    datetime.datetime(2015, 4, 20, 12, 15, 6), 
    datetime.datetime(2015, 4, 20, 12, 15, 21)], 
'temp_3': [datetime.datetime(2015, 4, 20, 12, 14, 36), 
    datetime.datetime(2015, 4, 20, 12, 14, 51), 
    datetime.datetime(2015, 4, 20, 12, 15, 6), 
    datetime.datetime(2015, 4, 20, 12, 15, 21)]} 

的xticks標籤是這樣的：

Answer 1

我終於發現了這一點：

ax.xaxis.set_major_formatter(DateFormatter('%H:%M')) 

here。

---

更重要的是，作爲上述解決方案已不縮小時顯示天：

from matplotlib.dates import AutoDateFormatter, AutoDateLocator 

xtick_locator = AutoDateLocator() 
xtick_formatter = AutoDateFormatter(xtick_locator) 
xtick_formatter.scaled[30.] = '%d %b' 
xtick_formatter.scaled[1.] = '%d %b' 
xtick_formatter.scaled[1/24.] = '%d/%m %H:%M' 
xtick_formatter.scaled[1/(24.*60.)] = '%d/%m %H:%M' 
xtick_formatter.scaled[1/(24.*60.*60.)] = '%d/%m %H:%M:%S' 
ax_av.xaxis.set_major_locator(xtick_locator) 
ax_av.xaxis.set_major_formatter(xtick_formatter) 

This幫助了很多（雖然不帶參數的AutoDateFormatter的例子不工作對我來說）