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| Started by | Robert <rxjwg98@gmail.com> |
|---|---|
| First post | 2016-01-02 04:44 -0800 |
| Last post | 2016-01-02 07:41 -0800 |
| Articles | 3 — 3 participants |
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What meaning is '[: , None]'? Robert <rxjwg98@gmail.com> - 2016-01-02 04:44 -0800
Re: What meaning is '[: , None]'? Steven D'Aprano <steve@pearwood.info> - 2016-01-03 02:39 +1100
Re: What meaning is '[: , None]'? Rustom Mody <rustompmody@gmail.com> - 2016-01-02 07:41 -0800
| From | Robert <rxjwg98@gmail.com> |
|---|---|
| Date | 2016-01-02 04:44 -0800 |
| Subject | What meaning is '[: , None]'? |
| Message-ID | <5607ba13-100b-411c-824a-de80c3c52e33@googlegroups.com> |
Hi, I read a code snippet, in which object w_A is: w_A Out[48]: array([ 0.10708809, 0.94933575, 0.8412686 , 0.03280939, 0.59985308]) Then, I don't know what is '[: ' below: vs_A = w_A[:, None] * xs I don't find the answer after searching around Could you explain above code to me? Thanks,
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| From | Steven D'Aprano <steve@pearwood.info> |
|---|---|
| Date | 2016-01-03 02:39 +1100 |
| Message-ID | <5687ef39$0$1588$c3e8da3$5496439d@news.astraweb.com> |
| In reply to | #101142 |
On Sat, 2 Jan 2016 11:44 pm, Robert wrote: > Hi, > > I read a code snippet, in which object w_A is: > > > w_A > Out[48]: array([ 0.10708809, 0.94933575, 0.8412686 , 0.03280939, > 0.59985308]) w_A looks like a numpy array of five values. http://docs.scipy.org/doc/numpy/reference/arrays.html > Then, I don't know what is '[: ' below: > vs_A = w_A[:, None] * xs The syntax w_A[ ... ] is a "slice" of array w_A. Slicing means to create a new array from part of the original. None inside a numpy slice behaves as an alias for numpy.newaxis. http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html In this case, w_A[:, None] returns a "view" of the original w_A array. -- Steven
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| From | Rustom Mody <rustompmody@gmail.com> |
|---|---|
| Date | 2016-01-02 07:41 -0800 |
| Message-ID | <335bf0cc-b25e-43b6-be0a-94a94ce0eb73@googlegroups.com> |
| In reply to | #101142 |
On Saturday, January 2, 2016 at 6:14:24 PM UTC+5:30, Robert wrote: > Hi, > > I read a code snippet, in which object w_A is: > > > w_A > Out[48]: array([ 0.10708809, 0.94933575, 0.8412686 , 0.03280939, 0.59985308]) > > > Then, I don't know what is '[: ' below: > vs_A = w_A[:, None] * xs > > > I don't find the answer after searching around > Could you explain above code to me? > Thanks, You probably want to search for 'slice/slicing' and 'indexing' I get this http://docs.scipy.org/doc/numpy-1.10.0/reference/arrays.indexing.html [Note: I dont know much about this]
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