Using common NumPy functions on dnpdata objects

This example demonstrates how to use common numpy functions to manipulate dnpdata objects.

Note, this is still an experimental feature.

How numpy array functions are operating on DNPData

Many numpy functions can directly be used on DNPData. What the function returns depends on the result:

• when the result is a scalar a salar is returned

• when the result is a ndarray a DNPData object is returned

when the axis keyword is support by the numpy function one can provide the dimension (e.g. np.sum(mydata, axis='f2')) The corresponding axis is consumed and no longer in the returned DNPData object. The following example shows how this can be conveniently used.

To get started, first, setup the python environment:

import dnplab as dnp
import numpy as np
import matplotlib.pyplot as plt

Let's load some example data the data consists of 4 fid that are phase cycled (0-90-180-270)

data = dnp.load("../../data/prospa/water_phase_cycled/data.2d")

we are interested in the spectra

data = dnp.fourier_transform(data)

since we don't know what the spectra is made of, we want to have a quick look at the magnitude:

data_magn = np.abs(data)

and lets plot the magnitude spectrum for all 4 cycles

dnp.fancy_plot(data_magn)

[<matplotlib.lines.Line2D object at 0x7f29ee98c490>, <matplotlib.lines.Line2D object at 0x7f29ee98c670>, <matplotlib.lines.Line2D object at 0x7f29ee98cbe0>, <matplotlib.lines.Line2D object at 0x7f29ee98c730>]

since the spectra are phase cycled the mean of the real part of the spectrum should be 0. Let's check and plot that:

mean_real_spectrum = np.real(np.mean(data, axis="Average"))
total_mean = np.mean(mean_real_spectrum)
average_in_dims = "Average" in mean_real_spectrum.dims
print("The sum of the mean spectrum is {0} ".format(total_mean))
print("Average in mean_real_spectrum.dims: {0}".format(average_in_dims))
dnp.fancy_plot(mean_real_spectrum)

The sum of the mean spectrum is -1.037494719028472
Average in mean_real_spectrum.dims: False

[<matplotlib.lines.Line2D object at 0x7f29f0c262e0>]

the total mean could also be calculated directly using np.mean() without the axis keyword (up to numerical precision)

print(np.mean(np.real(data)), "~=", total_mean)
dnp.plt.show()

-1.037494719028473 ~= -1.037494719028472