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

#%% make some data frame for testing

phi = np.linspace(0, 2*np.pi, 1024)
df = pd.DataFrame({
    'cos': np.cos(phi),
    'sin': np.sin(phi),
    'cosxsin': np.cos(phi) * np.sin(phi)
}, index=phi)

#%% function which resamples a dataframe to a new number of rows
def resample_fixed(df, n_new):
  n_old, m = df.values.shape
  mat_old = df.values
  mat_new = np.zeros((n_new, m))
  x_old = np.linspace(df.index.min(), df.index.max(), n_old)
  x_new = np.linspace(df.index.min(), df.index.max(), n_new)

  for j in range(m):
      y_old = mat_old[:, j]
      y_new = np.interp(x_new, x_old, y_old)
      mat_new[:, j] = y_new

  return pd.DataFrame(mat_new, index=x_new, columns=df.columns)

#%% resample the data frame and show the values

df2 = resample_fixed(df, 100)
print(df2.shape)
df2.plot()