matplotlib: Insert comment on timeline graph
Inserting a comment into the time axis graph (ʻaxis.text () , ʻaxis.annotate ()) is specified by time on the target axis [^ 1].
[^ 1]: In the example below, the X axis is the time axis
comment.py
import sys
import matplotlib as mpl
mpl.use('Agg')
import matplotlib.pyplot as plt
import matplotlib.dates as dates
from datetime import datetime as dt
import pandas as pd
fig, ax = plt.subplots()
ax.xaxis_date()
ax.set_xlim([dt(2017,1,1),dt(2017,1,14)])
ax.set_ylim([0,100])
ax.grid(True)
ax.text(dt(2017,1,3,12,0), 53, "Datetime")
ax.text(pd.Timestamp("2017-1-5"), 40, "Pandas")
ax.text(736340, 70, "Number") #1
plt.xticks(rotation=45)
fig.subplots_adjust( bottom=0.15, top=0.95,left=0.1, right=0.95)
plt.savefig("comment.png ")
python
$ python comment.py
Either datetime or pd.Timestamp is fine.
About the numerical value used for the time axis
Matplotlib provides sophisticated date plotting capabilities, standing on the shoulders of python datetime, the add-on modules pytz and dateutil. datetime objects are converted to floating point numbers which represent time in days since 0001-01-01 UTC, plus 1. For example, 0001-01-01, 06:00 is 1.25, not 0.25. The helper functions date2num(), num2date() and drange() are used to facilitate easy conversion to and from datetime and numeric ranges.
That's right.
2016-12-31 00:00:00 (UTC) including leap years, let's roughly calculate,
python
$ perl -le '$a += ($_ % 4 == 0 and $_ % 100 == 0 and $_ % 400 != 0 )? 365 : $_ % 4 == 0 ? 366 : 365 for 1 .. 2016 ; print $a'
736329
$ python -c 'import matplotlib.dates as md ; print(md.num2date(736329))'
2016-12-31 00:00:00+00:00
Will be. So, # 1 above is the same as specifying 2017-01-11 00: 00: 00 + 00.
For hours, minutes, and seconds, [^ 2] after the decimal point. [^ 2]: If it was 9:00:05, (9 * 60 * 60 + 5) / (24 * 60 * 60)
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