CODEWITHSUNDEEP
pythonpandasmatplotlibscipy
cbornes
cbornes

Reputation: 56

Find local maxima in data from dataframe

Is there a way to find the local maxima from data I get from CSV file and put its value on the plot?

The x and y values that are in a pandas dataframe look something like this

x = 1598.78, 1596.85, 1594.92, 1592.99, 1591.07, 1589.14, 1587.21, 1585.28, 1583.35, 1581.42, 1579.49, 1577.57, 1575.64, 1573.71, 1571.78, 1569.85, 1567.92, 1565.99, 1564.07, 1562.14, 1560.21, 1558.28, 1556.35, 1554.42, 1552.49, 1550.57, 1548.64, 1546.71, 1544.78, 1542.85, 1540.92, 1538.99, 1537.07, 1535.14, 1533.21, 1531.28, 1529.35, 1527.42, 1525.49, 1523.57, 1521.64, 1519.71, 1517.78, 1515.85, 1513.92, 1511.99, 1510.07, 1508.14, 1506.21, 1504.28, 1502.35, 1500.42, 1498.49, 1496.57, 1494.64, 1492.71, 1490.78, 1488.85, 1486.92, 1484.99, 1483.07, 1481.14, 1479.21, 1477.28, 1475.35, 1473.42, 1471.49, 1469.57, 1467.64, 1465.71, 1463.78, 1461.85, 1459.92, 1457.99, 1456.07, 1454.14, 1452.21, 1450.28, 1448.35, 1446.42, 1444.49, 1442.57, 1440.64, 1438.71, 1436.78, 1434.85, 1432.92, 1430.99, 1429.07, 1427.14, 1425.21, 1423.28, 1421.35, 1419.42, 1417.49, 1415.57, 1413.64, 1411.71, 1409.78, 1407.85, 1405.92, 1403.99, 1402.07, 1400.14
 
y = 0.640, 0.624, 0.609, 0.594, 0.581, 0.569, 0.558, 0.547, 0.537, 0.530, 0.523, 0.516, 0.508, 0.502, 0.497, 0.491, 0.487, 0.484, 0.481, 0.480, 0.479, 0.482, 0.490, 0.503, 0.520, 0.542, 0.566, 0.586, 0.600, 0.606, 0.593, 0.569, 0.557, 0.548, 0.538, 0.531, 0.527, 0.524, 0.522, 0.522, 0.523, 0.525, 0.526, 0.527, 0.530, 0.534, 0.536, 0.539, 0.547, 0.553, 0.557, 0.563, 0.573, 0.599, 0.654, 0.738, 0.852, 0.891, 0.810, 0.744, 0.711, 0.694, 0.686, 0.683, 0.683, 0.690, 0.700, 0.706, 0.713, 0.723, 0.731, 0.732, 0.737, 0.756, 0.779, 0.786, 0.790, 0.794, 0.802, 0.815, 0.827, 0.832, 0.831, 0.826, 0.823, 0.828, 0.834, 0.834, 0.832, 0.832, 0.831, 0.825, 0.816, 0.804, 0.798, 0.794, 0.786, 0.775, 0.764, 0.752, 0.739, 0.722, 0.708, 0.697

and I'm trying to get something like this.

enter image description here

P.S. Note that numeric values were added with the plt.text function just to exemplify what I want.

Upvotes: 1

Views: 114

Answers (1)

Ashish Jain
Ashish Jain

Reputation: 467

x = [1598.78, 1596.85, 1594.92, 1592.99, 1591.07, 1589.14, 1587.21, 1585.28, 1583.35, 1581.42, 1579.49, 1577.57, 1575.64, 1573.71, 1571.78, 1569.85, 1567.92, 1565.99, 1564.07, 1562.14, 1560.21, 1558.28, 1556.35, 1554.42, 1552.49, 1550.57, 1548.64, 1546.71, 1544.78, 1542.85, 1540.92, 1538.99, 1537.07, 1535.14, 1533.21, 1531.28, 1529.35, 1527.42, 1525.49, 1523.57, 1521.64, 1519.71, 1517.78, 1515.85, 1513.92, 1511.99, 1510.07, 1508.14, 1506.21, 1504.28, 1502.35, 1500.42, 1498.49, 1496.57, 1494.64, 1492.71, 1490.78, 1488.85, 1486.92, 1484.99, 1483.07, 1481.14, 1479.21, 1477.28, 1475.35, 1473.42, 1471.49, 1469.57, 1467.64, 1465.71, 1463.78, 1461.85, 1459.92, 1457.99, 1456.07, 1454.14, 1452.21, 1450.28, 1448.35, 1446.42, 1444.49, 1442.57, 1440.64, 1438.71, 1436.78, 1434.85, 1432.92, 1430.99, 1429.07, 1427.14, 1425.21, 1423.28, 1421.35, 1419.42, 1417.49, 1415.57, 1413.64, 1411.71, 1409.78, 1407.85, 1405.92, 1403.99, 1402.07, 1400.14]
 
y = [0.640, 0.624, 0.609, 0.594, 0.581, 0.569, 0.558, 0.547, 0.537, 0.530, 0.523, 0.516, 0.508, 0.502, 0.497, 0.491, 0.487, 0.484, 0.481, 0.480, 0.479, 0.482, 0.490, 0.503, 0.520, 0.542, 0.566, 0.586, 0.600, 0.606, 0.593, 0.569, 0.557, 0.548, 0.538, 0.531, 0.527, 0.524, 0.522, 0.522, 0.523, 0.525, 0.526, 0.527, 0.530, 0.534, 0.536, 0.539, 0.547, 0.553, 0.557, 0.563, 0.573, 0.599, 0.654, 0.738, 0.852, 0.891, 0.810, 0.744, 0.711, 0.694, 0.686, 0.683, 0.683, 0.690, 0.700, 0.706, 0.713, 0.723, 0.731, 0.732, 0.737, 0.756, 0.779, 0.786, 0.790, 0.794, 0.802, 0.815, 0.827, 0.832, 0.831, 0.826, 0.823, 0.828, 0.834, 0.834, 0.832, 0.832, 0.831, 0.825, 0.816, 0.804, 0.798, 0.794, 0.786, 0.775, 0.764, 0.752, 0.739, 0.722, 0.708, 0.697]

import matplotlib.pyplot as plt

# The slope of a line is a measure of its steepness. Mathematically, slope is calculated as "rise over run" (change in y divided by change in x).
slope = [np.sign((y[i] - y[i-1]) / (x[i] - x[i-1])) for i in range(1, len(y))]

x_prev = slope[0]
optima_dic={'minima':[], 'maxima':[]}
for i in range(1, len(slope)):
    if slope[i] * x_prev == -1: #slope changed
        if x_prev == 1: # slope changed from 1 to -1
            optima_dic['maxima'].append(i)
        else: # slope changed from -1 to 1
            optima_dic['minima'].append(i)
        x_prev=-x_prev

from matplotlib.pyplot import text

plt.rcParams["figure.figsize"] = (20,10)
ix = 0
for x_, y_ in zip(x, y):
    plt.plot(x_, y_, 'o--', color='grey')
    if(ix in optima_dic['minima']):
        plt.text(x_, y_, s = x_, fontsize=10)
    ix += 1

plot

Upvotes: 1

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