CODEWITHSUNDEEP
pythonpandasmatplotlib
Sam Sims
Sam Sims

Reputation: 59

Using matplotlib to plot time on my x axis, however it starts from 0, not the actual start time

I have a CSV file with time data as follows:

Time,Download,Upload 17:00,7.51,0.9 17:15,6.95,0.6 17:31,5.2,0.46

I import the csv into a pandas dataframe: df = pd.read_csv('speeds.csv', parse_dates=['Time'])

And then plot the graph like so:

fig, ax = plt.subplots(figsize=(20, 7))
df.plot(ax=ax)
majorFmt = mdates.DateFormatter('%H:%M:')
minorFmt = mdates.DateFormatter('%H:%M:')
hour_locator = mdates.HourLocator()
min_locator = mdates.MinuteLocator(byminute=[15, 30, 45])
ax.xaxis.set_major_locator(hour_locator)
ax.xaxis.set_major_formatter(majorFmt)
plt.setp(ax.xaxis.get_majorticklabels(), rotation=90, fontsize=10)
ax.xaxis.set_minor_locator(min_locator)
ax.xaxis.set_minor_formatter(minorFmt)
plt.setp(ax.xaxis.get_minorticklabels(), rotation=90, fontsize=8)

However the final graph starts from 00:00 like so, although the CSV file starts at 17:00:Graph

How comes the graph doesnt start at 17:00 also?

Another problem (while im here) is the major lables dont line up with the major markers, they are shifted left slightly how would I fix that?

Upvotes: 0

Views: 659

Answers (1)

Stef
Stef

Reputation: 30579

First question - graph doesn't start at 17:00:

Your csv only gives times (no dates) and it rolls over midnight. Pandas implicitely adds the current date to all times, so that times after midnight, which pertain to the next day, get the same date a times before midnight. Therefore you'll have to adjust the date part:

days = 0
df['Datetime']=df['Time']
for i in df.index:
   if i > 0 and df.at[i,'Time'] < df.at[i-1,'Time']:
      days += 1
   df.at[i,'Datetime'] = df.at[i,'Time'] + DateOffset(days=days)

and then use the Datetime column on your x axis.

Second question - shifted major markers:

Set horizontal alingment

plt.setp(ax.xaxis.get_majorticklabels(), rotation=90, fontsize=10, horizontalalignment='center')

Upvotes: 1

Related Questions