: column in front of variable

Question

Oops, coming back with the column question before the variable. Example I’m seeing in python in neural recurring. arr = arr[:n_batches * batches_size] what the :n_batches ?

Answer 1

It’s called Slice. With it you can access a slice of an object that is eternal. For example, do lista[1:5] you would be accessing items 1 to 4 (the 5 represents the first index not included in the slice). When omitted the first value, the slice from the beginning of the iterator will be considered. That is, do lista[:5] is the equivalent of lista[0:5]. If the second value is omitted, it will be considered until the end of the second value. That is, do lista[5:] would take all values from index 5 to the end. If both numbers are omitted, you will take the iterator from start to finish, making an Raza copy of your object.

In your case,

arr = arr[:n_batches * batches_size]

You are accessing the eternal arr from start to multiplication result n_batches * batches_size. The equivalent would be:

arr = arr[0:n_batches * batches_size]

See some other examples:

lista = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

print(lista[1:5])  # [1, 2, 3, 4]
print(lista[:5])   # [0, 1, 2, 3, 4]
print(lista[1:])   # [1, 2, 3, 4, 5, 6, 7, 8, 9]
print(lista[:])    # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

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