Warm tip: This article is reproduced from serverfault.com, please click
arrays numpy python tensorflow

Set values in row to zero before index value of row [NumPy or Tensorflow]

发布于 2020-11-28 00:17:33

I have an array A with shape (N,). I am taking N=5 for illustration:

A = np.array([0,1,1,0,1])

And I want to transform it to the following NxN matrix B. Solutions in both NumPy and Tensorflow are good but the latter is preferred.

B = np.array([[0,1,1,0,1],
              [0,1,1,0,1],
              [0,1,1,0,1],
              [0,0,0,0,1],
              [0,0,0,0,1]])

One solution can be comprised of following steps:

  1. Repeat array A N times
  2. Loop through each row i. Look for the index of the last zero until the i-th element of that row.
  3. Replace all elements preceding that index with zeros.

Another illustration with N=10:

D = np.array([0,1,1,1,0,0,1,1,0,0])

E = np.array([[0,1,1,1,0,0,1,1,0,0],
              [0,1,1,1,0,0,1,1,0,0],
              [0,1,1,1,0,0,1,1,0,0],
              [0,1,1,1,0,0,1,1,0,0],
              [0,0,0,0,0,0,1,1,0,0],
              [0,0,0,0,0,0,1,1,0,0],
              [0,0,0,0,0,0,1,1,0,0],
              [0,0,0,0,0,0,1,1,0,0],
              [0,0,0,0,0,0,0,0,0,0],
              [0,0,0,0,0,0,0,0,0,0]])
Questioner
rafiko1
Viewed
0
分享
fdermishin 2020-11-28 18:16:29 
A = np.array([0,1,1,0,1])
N = A.shape[0]
column = (A > 0).reshape((N, 1))
mask = np.ones((N, N), dtype=np.bool)
mask = np.where(column, False, np.tril(mask, -1))
mask = np.cumsum(mask, axis=0)
B = np.where(mask, 0, np.tile(A, (N, 1)))

[[0 1 1 0 1]
 [0 1 1 0 1]
 [0 1 1 0 1]
 [0 0 0 0 1]
 [0 0 0 0 1]]

Explanation

  1. Compute lower triangular matrix
[[False False False False False]
 [ True False False False False]
 [ True  True False False False]
 [ True  True  True False False]
 [ True  True  True  True False]]
  1. Find ones in A and fill corresponding rows with False
[[False False False False False]
 [False False False False False]
 [False False False False False]
 [ True  True  True False False]
 [False False False False False]]
  1. Compute cumulative sum to set zeros to all rows below. This is a mask of all elements that should be zeroed out
[[0 0 0 0 0]
 [0 0 0 0 0]
 [0 0 0 0 0]
 [1 1 1 0 0]
 [1 1 1 0 0]]
  1. Repeat array A N times
[[0 1 1 0 1]
 [0 1 1 0 1]
 [0 1 1 0 1]
 [0 1 1 0 1]
 [0 1 1 0 1]]
  1. Mask its elements
[[0 1 1 0 1]
 [0 1 1 0 1]
 [0 1 1 0 1]
 [0 0 0 0 1]
 [0 0 0 0 1]]

热门github

1
A multi-platform library for OpenGL, OpenGL ES, Vulkan, window and input
2
Dev tool that writes scalable apps from scratch while the developer oversees the implementation
3
shadcn/ui, but for Svelte. ✨
4
The Python Risk Identification Tool for generative AI (PyRIT) is an open access automation framework to empower security professionals and machine learning engineers to proactively find risks in their generative AI systems.
5
Performance-portable, length-agnostic SIMD with runtime dispatch
6
ZK Credo
7
OpenCodeInterpreter: Integrating Code Generation with Execution and Refinement
8
Joplin - the secure note taking and to-do app with synchronisation capabilities for Windows, macOS, Linux, Android and iOS.
9
Mamba is a new state space model architecture showing promising performance on information-dense data such as language modeling, where previous subquadratic models fall short of Transformers. It is based on the line of progress on structured state space models, with an efficient hardware-aware design and implementation in the spirit of FlashAttention.
10
This repository contains System Design resources which are useful while preparing for interviews and learning Distributed Systems
11
Curso para aprender el lenguaje de programación Python desde cero y para principiantes. 75 clases, 37 horas en vídeo, código, proyectos y grupo de chat. Fundamentos, frontend, backend, testing, IA...
12
🎓 Path to a free self-taught education in Computer Science!
13
1️⃣🐝🏎️ The One Billion Row Challenge -- A fun exploration of how quickly 1B rows from a text file can be aggregated with Java
14
A collective list of free APIs
15
📚 Freely available programming books