难以将 str 数据转换为 int/float/decimal 以使用 matplolib 进行绘图

Question

I have extracted data from a SQL database table but have been having persistent issues with trying to plot a graph between two variables. This is due to conversion issue between data types. I have first successfully converted a list to a str data type and now I want to convert it to either a float / int / decimal type so that I can use it with matplotlib. I feel stuck at the moment since I am unable to convert the str data to any of them. Shown below is my script:

import mysql.connector as mariadb
import matplotlib as mpl
mpl.use('Agg')
import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
from matplotlib import pyplot
from decimal import Decimal
import pandas as pd

mariadb_connection = mariadb.connect(user='user', password='password', database='mydatabase')
cur = mariadb_connection.cursor()
cur.execute("SELECT time, current FROM table1")

current = []
time = []

for row in cur.fetchall():
    current.append(int(row[1]))
    time.append(str(row[0]))

print(type(time)) #at this point terminal shows it is a list data type
time = pd.to_datetime(time)
print(type(time)) #at this point terminal shows it is a <class 'pandas.core.indexes.datetimes.DatetimeIndex'>data type

print(type(current))  #at this point, terminal shows it is a list data type
current=','.join(str(v) for v in current)
print(type(current)) #at this point, terminal shows it is a str data 
current=float(current) #at this point, I get an error stating ValueError: invalid literal for float()
print(type(current))

mariadb_connection.close()

plt.figure()
plt.plot(time, current) 

plt.show()
fig.savefig('plot.jpg')

On running this script, I get an error stating ValueError: invalid literal for float(): 51,52,52,53,52,52,53,53,55,54,58,72,63,68,79,140,133,102,116,120,189,196,151,249,277,218,206,210,212,173,194,216,181,166,221,212,175,189,288,300,281,210,266

I then modified the line current=float(current) to current=int(current) to try converting the str data to int type and it states another error ValueError: invalid literal for int() with base 10: '51,52,52,53,.....

I then also tried to convert my current variables to decimal type by changing that line to current=decimal(current) but I get decimal.InvalidOperation: Invalid literal for Decimal: '51,52,52....

Any advice on how I can convert my current values to int / float / decimal type?

Updates : There is no need to go through the conversion steps for the current variable. Apparently, just using the integer list with pandas plotting is sufficient to get a plot.

Answer 1

If you want to use pandas, this will work:

import pandas as pd 

# this is the data you gave (only five values)  
time = ['2017-12-27 12:53:00', '2017-12-27 13:19:00', '2017-12-27 13:20:00', '2017-12-27 13:25:00', '2017-12-27 13:30:00']
current = [51, 52, 52, 53, 52]

df = pd.DataFrame(current, index=time)
df.plot()