matplotlib ticks与数据点不对齐

Question

我修改了the example但是如果设置nbins = 10，则x刻度标记位置似乎不正确！但如果设置nbins = 5，它可以正常工作。我有什么问题？

#!/usr/bin/env python
import numpy as np
import matplotlib.pyplot as plt
from time import mktime
from datetime import datetime
from matplotlib.ticker import MaxNLocator
#%matplotlib inline
#-----------------------------------------#
def main():
    ticks = [ "9-28 11:07:57.435", "9-28 11:10:00.123", "9-28 11:40:00.654", "9-28 11:50:00.341", "9-28 12:00:00.773"]
    y = np.array([10, 12, 9, 15, 11])
    x = [mktime(datetime.strptime("2014-"+i, "%Y-%m-%d %H:%M:%S.%f").timetuple()) for i in ticks]
    plt.stem(x,y)
    plt.xticks(x, ticks,rotation=25,ha='right')
    plt.gca().xaxis.set_major_locator(MaxNLocator(nbins=10, prune = 'lower'))
    plt.gca().spines['right'].set_color('none')
    plt.gca().spines['top'].set_color('none')
    plt.gca().spines['left'].set_smart_bounds(True)
    plt.gca().spines['bottom'].set_smart_bounds(True)
    plt.gca().xaxis.set_ticks_position('bottom')
    plt.gca().yaxis.set_ticks_position('left')
    plt.show()
    return

#-----------------------------------------#
if __name__ == "__main__":
    main()

Answer 1

当您指定plt.xticks时，它的作用是将刻度定位器设置为 FixedLocator ，允许您明确地放置刻度。然后，当您将刻度定位器分配给 MaxNLocator 时，您将覆盖显式刻度位置。

要获得最多N个刻度，您可以从刻度列表中提取N个值，然后将这些值传递给xticks，并取消手动设置定位器。这些行从当前的5个列表中拉出3个滴答作为示例。

inds = np.linspace(0,len(ticks)-1,3).astype(int)
plt.xticks(np.array(x)[inds], np.array(ticks)[inds],rotation=25,ha='right')

Answer 2

以下一种解决方案：

#!/usr/bin/env python
#%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from time import mktime
from datetime import datetime

#-----------------------------------------#
def main():
    x = [
"9-28 11:07:57.435",
"9-28 11:10:00.123",
"9-28 11:40:00.654",
"9-28 11:50:00.341",
"9-28 12:00:00.773"
]
    y = np.array([10, 12, 9, 15, 11])
    dtlst = str2dt(x)
    plt.stem(dt2float(dtlst),y)
    bins = 5
    dtlst = list(linspace(dtlst[0],dtlst[-1],bins))
    plt.xticks(dt2float(dtlst),dt2str(dtlst),rotation=25,ha='right')
    plt.gca().spines['right'].set_color('none')
    plt.gca().spines['top'].set_color('none')
    plt.gca().spines['left'].set_smart_bounds(True)
    plt.gca().spines['bottom'].set_smart_bounds(True)
    plt.gca().xaxis.set_ticks_position('bottom')
    plt.gca().yaxis.set_ticks_position('left')
    plt.show()
    return

def str2dt(strlst):
    dtlst = [datetime.strptime("2014-"+i, "%Y-%m-%d %H:%M:%S.%f") for i in strlst]
    return dtlst

def dt2float(dtlst):
    floatlst = [mktime(dt.timetuple()) for dt in dtlst]
    return floatlst

def dt2str(dtlst):
    dtstr = [dt.strftime("%Y-%m-%d %H:%M:%S %Z%z") for dt in dtlst]
    return dtstr

def float2dt(floatlst):
    dtlst = [datetime.fromtimestamp(seconds) for seconds in floatlst]
    return dtlst

def linspace(start, end, bins):
    delta = (end - start)/bins
    x = start
    while x <= end:
        yield x
        x = x + delta
    return

#-----------------------------------------#
if __name__ == "__main__":
    main()
#-----------------------------------------#

输出：