如何 plot 数据，x 轴上的时间不是日期时间

Question

   id        timestamp          energy
0   a   2012-03-18 10:00:00     0.034
1   b   2012-03-20 10:30:00     0.052
2   c   2013-05-29 11:00:00     0.055
3   d   2014-06-20 01:00:00     0.028
4   a   2015-02-10 12:00:00     0.069

I want to plot these data like below. just time on x-axis, not date nor datetime.

because I want to see the values per each hour.

https://i.stack.imgur.com/u73eJ.png

but this code plot like this.

plt.plot(df['timestamp'], df['energy'])

https://i.stack.imgur.com/yd6NL.png

I tried some codes but they just format the X data hide date part and plot like second graph.

+ df['timestamp'] is datetime type.

what should I do? Thanks.

Answer 1

you can convert your datetime into time, if your df["timestamp"] is already in datetime format then

df["time"] = df["timestamp"].map(lambda x: x.time())
plt.plot(df['time'], df['energy'])

if df["timestamp"] is of type string then you can add one more line in front as df["timestamp"] = pd.to_datetime(df["timestamp"])

Update: look like matplotlib does not accept time types, just convert to string

df["time"] = df["timestamp"].map(lambda x: x.strftime("%H:%M"))
plt.scatter(df['time'], df['energy'])

Answer 2

First check, if type of df["timestamp"] is in datetime format. if not

import pandas as pd  
time = pd.to_datetime(df["timestamp"])
print(type(time))

Then,

import matplotlib.pyplot as plt
values = df['energy']
plt.plot_date(dates , values )
plt.xticks(rotation=45)
plt.show()