Python: plot dataframe of datetime entries

Question

My data looks like this :

    900324492   900405679   900472531
1   2017-04-03 08:04:09 2017-04-03 07:49:53 2017-04-03 07:52:39
2   2017-04-03 08:05:36 2017-04-03 07:54:36 2017-04-03 07:52:19
3   2017-04-03 08:05:28 2017-04-03 07:43:00 2017-04-03 07:50:52
4   2017-04-03 08:06:05 2017-04-03 07:49:42 2017-04-03 07:53:55

So, for each column, I have a set of time stamps (datetime objects, to be exact). I like to make a scatter plot, where x is the df index or row number (i.e. x=[1,2,3,4,...]), and y is a time point. For example, If there are 4 rows and 10 columns in df, x axis should be 1, 2, 3, 4, and for x=1 there should be one point per entry in the first row.

It seemed like a simple task, but I'm struggling a bit. My code so far:

df = pd.read_csv('test.csv')
df2 = df.apply(lambda x : pd.to_datetime(x))

fig = plt.figure()                                                                                                                                                                                                                                                             
ax = fig.add_subplot(111)                                                                                                                                                                                                                                                      
y = df2.ix[:, 1]                                                                                                                                                                                                                                           
x = df2.index.values
# returns nonsense
ax.plot(x,y)
# TypeError: invalid type promotion
ax.scatter(x=x, y = df2.ix[:,1])
# TypeError: Empty 'DataFrame': no numeric data to plot
df2.ix[:,1].plot()

Test file link : test.csv

su79eu7k · Accepted Answer · 2017-04-05 02:58:32Z

1

Please check my example from yours. You should focus on to_pydatetime() and date2num() and np.nan. (You have to tag y axis to datetime format finally.)

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib.dates as dates


df = pd.read_csv('test.csv', header=None)
df2 = df.apply(lambda x : pd.to_datetime(x))

fig = plt.figure()                                                                                                                                                                                                                                                             
ax = fig.add_subplot(111)                                                                                                                                                                                                                                                      
y = df2.ix[:, 1]                                                                                                                                                                                                                                         
x = df2.index.values

def fix(x):
    try:
        return dates.date2num(x.to_pydatetime())
    except:
        return np.nan

y_lab = [str(e) for e in y]
y_ = [fix(e) for e in y]

ax.scatter(x=x, y=y_)

plt.yticks(y_, y_lab, rotation=0, size=6)
plt.show()

edited Apr 5, 2017 at 2:58

answered Apr 4, 2017 at 3:25

su79eu7k

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4 Comments

Alex Over a year ago

Thanks! But you see the y axis? It is not easy to interpret it, which kinda contradicts the motivation for doing it. Is there a way to fix it, so that it shows time, instead of decimals?

su79eu7k Over a year ago

You can use num2date() function for ylabel.

su79eu7k Over a year ago

I will show you an example after 3 hours! (AFK and currently mobile) So please hold on.

su79eu7k Over a year ago

Updated, sorry for late.

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