Can anyone pleas tell what's difference between (if a is some numppy object, lets say:array) a[1] and a[[1]]. If I understand correctly I can edit 1 element of a with a[[1]], but not with a[1]...any other difference? Is it also something like that with [] I just view some element(s) and with [[]] I make copy? If it's to any importance I'm using python 3.
1 Answer
When you say a[1] you are getting the element with index 1 (the second one) from a. a[[1]], on the other hand, is not a special syntax, it just means "get the elements of a indicated by the indices in the list [1]". You can also say a[[1, 2]], or use another array as index. The practical difference is that a[1] will be a single scalar element and a[[1]] will be an array with size 1 (assuming a had one dimension).
With respect to assignment, you will find that both a[1] = 2 and a[[1]] = 2 work equally well. This is because of NumPy's broadcasting semantics, which allow you to match objects of different dimensions seamlessly. However, the actual dimensions of a[1] and a[[1]] are different, and it does matter depending on the context.
You can read more about indexing in NumPy here.
