Python array access notation

Question

I have a very quick question about the notation on accessing an array in python.

Is this line:

trainPredictPlot[look_back:len(trainPredict) + look_back, :] = trainPredict

I've seen arrays are being accessed like this x[a:b] but never like this x[a:b,:]

Can someone explain me with detail what this line of code is doing? What does it mean to put colon before the closing bracket? What about the comma?

That is a NumPy slice. It is actually m[a:b, :]. Note the comma. See docs.scipy.org/doc/numpy/reference/arrays.indexing.html — Dan D.
– Dan D., Commented Mar 30, 2017 at 3:22

Guido · Accepted Answer · 2017-03-30 03:33:33Z

2

When you use x[a:b], it means that you are taking the elements from position "a" (x[a]) to position "b" (x[b]) of a one dimensional array. For the second case x[a:b,:], it is a two dimensional "a" to position "b" of the first dimension of the array, and all the elements of the second dimension of the array, in other words, from x[a][first element] to x[b][last element].

answered Mar 30, 2017 at 3:33

Guido

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Pablo Estrada Over a year ago

Thanks for your answer. Expanding on that notation then is it possible to add as many comas as dimensions my array has?

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