How variables are declared in python?

Question

I guess something is wrong with this I believe. I have an array of data set I'm trying to perform some analysis on. This is what I want to do. Say for example the following is the array

signal=[1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1...], I want to take the data points 0:3 stored somewhere, I need them and also replace those 0:3 with zeros. This is how I did it but the final result comes out right but the stored 0:3 data points stored also come out to be zeros. Can anyone help me out here. I thought it was something simple to do but I have been battling with this for the past couple of days. Thanks in advance!

here is my code:

n = len(signal)

for i in range(n):

    first_3points = signal[0:3]

    signal[0:3] = 0

    trancated_signal = signal

I will be very glad to see where I went wrong!

I don't see what the title of this question has to do with the problem at hand. — Matt Ball
– Matt Ball, Commented Jul 19, 2014 at 14:29
What is the loop for? Do you want overlapping or separate samples of length three? Or just the first three? The minimal fix could be signal[:3] = [0, 0, 0]. — jonrsharpe
– jonrsharpe, Commented Jul 19, 2014 at 15:03

Frank M · Accepted Answer · 2014-07-19 14:56:16Z

2

It looks like your application is better served with numpy, which is well-developed to work with arrays representing signal samples. You may already be using numpy, since if signal is a list, the assignment signal[0:3] = 0 raises a TypeError. Here's how I'd do it using numpy:

import numpy as np
N = 256
signal = np.ones(N)
first3 = signal[0:3].copy()
signal[0:3] = 0

Note that if you don't make first3 a copy of the first elements in signal, it just becomes a view into signal, and when you change elements in signal, you also change first3. If I understand your question correctly, you are trying to save the original elements from signal in first3 before you change them.

edited Jul 19, 2014 at 14:56

answered Jul 19, 2014 at 14:44

Frank M

1,59015 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user3843064 Over a year ago

frank128791, excellent it worked thanks a lot for your help. Yes I was to store that and make changes

Stuart · Accepted Answer · 2014-07-19 16:56:50Z

1

Using ordinary lists instead of numpy this is quite simple:

signal = [1] * 20
first_3_points = signal[:3]
signal[:3] = [0] * 3

The loop in your original code appears to be unnecessary.

answered Jul 19, 2014 at 16:56

Stuart

9,8771 gold badge24 silver badges34 bronze badges

Collectives™ on Stack Overflow

How variables are declared in python?

2 Answers 2

1 Comment

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Related