# Writing a pandas DataFrame to an Excel file

To create some data to write to a file, the following program generates a DataFrame with the height of a projectile launched at three different angles (in the columns) as a function of time (rows):

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

# Acceleration due to gravity, m.s-2.
g = 9.81

# Time grid, s.
t = np.linspace(0, 5, 500)
# Projectile launch angles, deg.
theta0 = np.array([30, 45, 80])
# Projectile launch speen, m.s-1.
v0 = 20

def z(t, v0, theta0):
"""Return the height of the projectile at time t > 0."""
return -g/2 * t**2 + v0*t*np.sin(theta0)

def x(t, v0, theta0):
"""Return the range of the projectile at time t > 0."""
return v0 * t * np.cos(theta0)

# An empty DataFrame with columns for the different launch angles.
df = pd.DataFrame(columns=theta0, index=t)
# Populate df with the projectile heights as a function of time.
for theta in theta0:
df[theta] = z(t, v0, np.radians(theta))
# Once the projectile has landed (z <= 0), set the height data as invalid.
df[df<=0] = np.nan

# Create a Matplotlib figure with the trajectories plotted.
fig, ax = plt.subplots()
for theta in theta0:
ax.plot(x(t, v0, np.radians(theta)), df[theta], label=f'${theta}^\circ$')

# The maximum height obtained by the projectile for each value of theta0.
heights = df.max()
print(heights)
# Set the y-limits with a bit of padding at the top; label the axes.
ax.set_ylim(0, heights.max()*1.05)
ax.set_xlabel('Range /m')
ax.set_ylabel('Height /m')
ax.legend()
plt.show()


The plot of the trajectories that is produced by this code is reproduced below. To save the DataFrame df to an Excel file in a single sheet, use to_excel:

df.to_excel('projectile.xlsx', sheet_name='Dependence on angle', )


To write an Excel file with more than one sheet, create a pd.ExcelWriter object and call to\_excel for each pandas object to output:

with pd.ExcelWriter('projectile2.xlsx') as writer:
for theta in theta0:
# Only retain the valid data for each trajectory.
ser = df[theta].dropna()
# Change the Series index to be the range instead of time.
ser.index = x(ser.index, v0, np.radians(theta))
ser.to_excel(writer, sheet_name=f'{theta} deg')