通过matplotlib.pyplot在Python中绘图（计算面积）

Question

I have a question \\ problem. I need to plot the graph by the numbers that I got from the file (which I did) and then I need to draw a line connecting start and end, and calculate the area that between these two lines. I try to make a lot of variations, but i have no idea how I can make it..

I'm trying do it via matplotlib.pyplot library

Here the 'figure' whitch I should to get after add 'connection line between beginning and and' and now I need calcutale square between black line and blue. PS the black one is kind of straight :)

Here is soure of code, and my data file... http://pastebin.com/g40bAzPR

#!/path/to/python -tt

# numerical data
# python GraphicalPart.py ../dataFile.txt

import sys
import matplotlib.pyplot as plt
import numpy as np

def startDivide(fileName):
 for i in range(1,2):
    inputFile = open(fileName)
    outputFile = open(fileName + "_" + str(i) + "_out.csv", "w")
    floatList = []
    for line in inputFile.readlines():
        data = line.split(" ")
        string = data[i]
        if string.startswith('-'): #remove '-'
            string = string[1:]
        floatList.append(float(string))

    floatList.sort() #sorting the list of data

    for item in floatList:
        outputFile.write("%s\n" % item)

    outputFile.close() 
    inputFile.close()

    data1=np.genfromtxt(fileName + "_" + str(i) + '_out.csv', skip_header=1)
    plt.plot(data1) 
    plt.savefig(fileName + "_" + str(i) + "_.png")
    plt.clf()

def main():
 if len(sys.argv) != 2:
  print "Not enough arguments. *_data.txt file only!"
 else:
  startDivide(sys.argv[1])

if __name__ == "__main__":
 main()

Answer 1

for i in range(1,2) is a loop which only iterates once. Maybe you plan on increasing the number of iterations? If so, bear in mind that it's quicker to load the data once , rather than multiple times in a for-loop. You can do that using np.genfromtxt with the usecols parameter to specify the desired columns.

To find the area under the curve, you could use np.trapz . To find the area between two curves, you subtract area under the upper curve from the area under the lower curve. Assuming the diagonal line is always above the data curve:

import sys
import matplotlib.pyplot as plt
import numpy as np

def startDivide(filename):
    data = np.genfromtxt(filename, dtype=None, usecols=[1])
    data = np.abs(data)
    data.sort()
    np.savetxt("{}_1_out.csv".format(filename), data)
    plt.plot(data)
    plt.plot([0,len(data)-1], [data[0], data[-1]])
    plt.savefig("{}_1_.png".format(filename))
    area = np.trapz([data[0], data[-1]], dx=len(data)-1) - np.trapz(data)
    print(area)

if __name__ == "__main__":
    startDivide(sys.argv[1])