更换已经比一些值的Python的numpy的阵列中的所有元素 [英] Replace all elements of Python NumPy Array that are greater than some value
问题描述
我有一个2D numpy的阵列,并想以255.0替换所有值在它大于或等于一个阈值T。据我所知,最根本的办法是:
形状= arr.shape
结果= np.zeros(形状)
对于在范围X(0,形状[0]):
对于在范围Y(0,形状[1]):
如果ARR [X,Y]> = T:
结果[X,Y] = 255
-
什么是做到这一点的最简洁和Python的方式?
-
有一个更快的(可能不够简明和/或更少的Python化)的方式来做到这一点?
这将是一个窗口/级别调整子程序用于人体头部的MRI扫描的一部分。二维数组numpy的是图像的像素数据。
我认为既要做到这一点,最快,最简洁的方法是使用numpy的的内置索引。如果你有一个 ndarray
名为改编
可以取代所有元素> 255
用值 X
如下:
改编[ARR> 255] = X
我和一个500×500随机矩阵跑这在我的机器上,替换所有值> 0.5与5,并花了7.59ms平均。
在[1]:进口numpy的为NP
[2]:A = np.random.rand(500,500)
[3]:timeit A [A> 0.5] = 5
100圈,最好的3:每循环7.59毫秒
I have a 2D NumPy array and would like to replace all values in it greater than or equal to a threshold T with 255.0. To my knowledge, the most fundamental way would be:
shape = arr.shape
result = np.zeros(shape)
for x in range(0, shape[0]):
for y in range(0, shape[1]):
if arr[x, y] >= T:
result[x, y] = 255
What is the most concise and pythonic way to do this?
Is there a faster (possibly less concise and/or less pythonic) way to do this?
This will be part of a window/level adjustment subroutine for MRI scans of the human head. The 2D numpy array is the image pixel data.
I think both the fastest and most concise way to do this is to use Numpy's builtin indexing. If you have a ndarray
named arr
you can replace all elements >255
with a value x
as follows:
arr[arr > 255] = x
I ran this on my machine with a 500 x 500 random matrix, replacing all values >0.5 with 5, and it took an average of 7.59ms.
In [1]: import numpy as np
In [2]: A = np.random.rand(500, 500)
In [3]: timeit A[A > 0.5] = 5
100 loops, best of 3: 7.59 ms per loop
这篇关于更换已经比一些值的Python的numpy的阵列中的所有元素的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!