按日期突出显示python图中的最大点

Question

I know this question is really close to a lot of other answered questions, but all previous answers are giving me the same traceback issues.

I have a straightforward time series, and I'm trying to highlight the maximum point. I'm running into problems manipulating a Pandas Dataframe to obtain the maximum y value for plotting on a graph. I think I'm nearly there, but I think the parse_dates parameter of the pd.read_csv import is messing with my indexing.

When I import the dataset, I have a datetime column, and a wind_speed column. When I resample for the daily average, the title for the variable column disappears and the datetime column becomes uncallable.

Before taking the daily average:

In[12]: weather.head()
Out[12]:                                  wind_speed
            d_stamp_t_stamp                
            2017-07-26 00:05:09        1.31
            2017-07-26 00:35:13        1.62
            2017-07-26 01:05:05        1.50
        .......

After taking the daily average:

wind_avg = weather.wind_speed.resample('D').mean()

d_stamp_t_stamp
2017-09-01    3.870625
2017-09-02    4.386875
2017-09-03    5.426739
2017-09-04    2.718750
2017-09-05    3.407708

The label for the wind_speed column goes away, and I can't seem to sample that data anymore.

So this is the code for the time series I have so far:

## Import weather data.
weather = pd.read_csv('/Users/regina/university_projects/Themo_Data/Weather0717-0618.csv', 
                 parse_dates=[[0,1]], index_col=0)
wind_avg = weather.wind_speed.resample('D').mean()

## Wind Speed graph
windplot = wind_avg.plot(title="Wind Speed", figsize=(12,8), 
                        fontsize=12, marker='o', markersize=7)
windplot.set_xlabel("Date"),windplot.set_ylabel("Wind Speed in m/s")

Which gives me this graph with wind speed average on the y axis.

The problem comes when I try to annotate the maximum wind speed.

y0 = max(wind_avg.wind_speed)
xpos = wind_avg.wind_speed.index(y0)
x0 = (wind_avg.d_stamp_t_stamp[xpos])

    windplot.annotate(
                "Max Speed", xy=(x0,y0), ha='right',
                va='bottom', textcoords='offset points', bbox=dict(BoxStyle='Round, pad=0.5', fc='yellow',
                alpha=0.5), arrowprops=dict(facecolor='black', shrink=0.05))

I get an attribute error message like this:

Traceback (most recent call last):

  File "<ipython-input-15-5e45876c5ebc>", line 5, in <module>
    y0 = max(wind_avg.wind_speed)

  File "/Users/regina/anaconda3/lib/python3.6/site-packages/pandas/core/generic.py", line 4372, in __getattr__
    return object.__getattribute__(self, name)

AttributeError: 'Series' object has no attribute 'wind_speed'

Is there something about the way I'm resampling the wind_speed column that removes its label? Thank you all so much!

Answer 1

In the line

wind_avg = weather.wind_speed.resample('D').mean()

you apply resample to the single Pandas Series which is in the column wind_speed of your Dataframe, so you'll get a Series as return value:

type(wind_avg)
Out: pandas.core.series.Series

Try

weather_avg = weather.resample('D').mean()
type(weather_avg)
Out: pandas.core.frame.DataFrame

and you'll get your whole weather dataset resampled per days.