numpy-100 | 100 numpy exercises | Machine Learning library
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kandi X-RAY | numpy-100 Summary
100 numpy exercises (with solutions)
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QUESTION
I am practicing 100 Numpy exercises. Question 60 asks for how to tell if a given 2D array has null columns?
I am wondering whether it asks for checking a column fulled with 0 or fulled with nan?
2 Solutions I foundIf null columns stands for column with its value all equal to 0
, this answer satisfies.
ANSWER
Answered 2019-Apr-30 at 13:58NaN
or nan
, either way, is the same as null. Meaning that there is no data there.
According to this post,
he main reason to use NaN (over None) is that it can be stored with numpy's float64 dtype, rather than the less efficient object dtype
As you can see, None
, np.nan
and 0
all behave slightly differently.
QUESTION
I have some images for which I want to calculate the Minkowski/box count dimension to determine the fractal characteristics in the image. Here are 2 example images:
10.jpg
:
24.jpg
:
I'm using the following code to calculate the fractal dimension:
...ANSWER
Answered 2018-Mar-28 at 20:13With fractal dimension of something physical the dimension might converge at different stages to different values. For example, a very thin line (but of finite width) would initially seem one dimensional, then eventual two dimensional as its width becomes of comparable size to the boxes used.
Lets see the dimensions that you have produced:
What do you see? Well the linear fits are not so good. And the dimensions is going towards a value of two. To diagnose, lets take a look at the grey-scale images produced, with the threshold that you have (that is, 0.9):
The nature picture has almost become an ink blob. The dimensions would go to a value of 2 very soon, as the graphs told us. That is because we pretty much lost the image. And now with a threshold of 50?
With new linear fits that are much better, the dimensions are 1.6 and 1.8 for urban and nature respectively. Keep in mind, that the urban picture actually has a lot of structure to it, in particular on the textured walls.
In future good threshold values would be ones closer to the mean of the grey scale images, that way your image does not turn into a blob of ink!
A good text book on this is "Fractals everywhere" by Michael F. Barnsley.
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You can use numpy-100 like any standard Python library. You will need to make sure that you have a development environment consisting of a Python distribution including header files, a compiler, pip, and git installed. Make sure that your pip, setuptools, and wheel are up to date. When using pip it is generally recommended to install packages in a virtual environment to avoid changes to the system.
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