slice

问题 I'm looking for an efficient way of achieving this, which I think is a slicing-like operation: >>> mylist = range(100) >>>magicslicer(mylist, 10, 20) [0,1,2,3,4,5,6,7,8,9,30,31,32,33,34,35,36,37,38,39,60,61,62,63......,97,98,99] the idea is: the slicing gets 10 elements, then skips 20 elements, then gets next 10, then skips next 20, and so on. I think I should not use loops if possible, for the very reason to use slice is (I guess) to do the "extraction" efficiently in a single operation.

问题 As far as I can tell, this is not officially not possible, but is there a "trick" to access arbitrary non-sequential elements of a list by slicing? For example: >>> L = range(0,101,10) >>> L [0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100] Now I want to be able to do a,b = L[2,5] so that a == 20 and b == 50 One way besides two statements would be something silly like: a,b = L[2:6:3][:2] But that doesn't scale at all to irregular intervals. Maybe with list comprehension using the indices I want?

问题 I am working with survey data loaded from an h5-file as hdf = pandas.HDFStore('Survey.h5') through the pandas package. Within this DataFrame , all rows are the results of a single survey, whereas the columns are the answers for all questions within a single survey. I am aiming to reduce this dataset to a smaller DataFrame including only the rows with a certain depicted answer on a certain question, i.e. with all the same value in this column. I am able to determine the index values of all

问题 In Golang, what is the difference between var s []int and s := make([]int, 0) ? I find that both works, but which one is better? 回答1: In addition to fabriziom's answer, you can see more examples at "Go Slices: usage and internals", where a use for []int is mentioned: Since the zero value of a slice ( nil ) acts like a zero-length slice , you can declare a slice variable and then append to it in a loop: // Filter returns a new slice holding only // the elements of s that satisfy f() func

问题 How does one determine the position of an element present in slice? I need something like the following: type intSlice []int func (slice intSlice) pos(value int) int { for p, v := range slice { if (v == value) { return p } } return -1 } 回答1: Sorry, there's no generic library function to do this. Go doesn't have a straight forward way of writing a function that can operate on any slice. Your function works, although it would be a little better if you wrote it using range . If you happen to

问题 The below code is running for first three elements of the tuple of this list SS1=[(1, 2, 3, 4, 5), (1, 2, 3, 4, 6), (1, 2, 3, 5, 6), (1, 2, 4, 5, 6), (1, 3, 4, 5, 6), (2, 3, 4, 5, 6)] from collections import Counter c = Counter(elem[0:3] for elem in SS1) for k, v in c.items(): if (v > 0): print(k,v) and the output is: (1, 2, 3) 3 (1, 2, 4) 1 (1, 3, 4) 1 (2, 3, 4) 1 But my expectation is not just for first three tuple...i want the counter for tuple (0,2,3) or tuple (1,2,4) likewise i can pass

问题 I found following cone in a js plugin var container = document.getElementById( 'vs-container' ), wrapper = container.querySelector( 'div.vs-wrapper' ), sections = Array.prototype.slice.call( wrapper.querySelectorAll( 'section' ) ), links = Array.prototype.slice.call( container.querySelectorAll( 'header.vs-header > ul.vs-nav > li' ) ); I couldn't understand what does Array.prototype.slice.call() & wrapper.querySelectorAll( 'section' ) do in above code. I've not seen them before so I would like

问题 I found following cone in a js plugin var container = document.getElementById( 'vs-container' ), wrapper = container.querySelector( 'div.vs-wrapper' ), sections = Array.prototype.slice.call( wrapper.querySelectorAll( 'section' ) ), links = Array.prototype.slice.call( container.querySelectorAll( 'header.vs-header > ul.vs-nav > li' ) ); I couldn't understand what does Array.prototype.slice.call() & wrapper.querySelectorAll( 'section' ) do in above code. I've not seen them before so I would like

问题 I have a list of lists. Each sublist has a length that varies between 1 and 100. Each sublist contains a particle ID at different times in a set of data. I would like to form lists of all particle IDs at a given time. To do this I could use something like: list = [[1,2,3,4,5],[2,6,7,8],[1,3,6,7,8]] list2 = [item[0] for item in list] list2 would contain the first elements of each sublist in list. I would like to do this operation not just for the first element, but for every element between 1

问题 It seems I am getting lost in something potentially silly. I have an n-dimensional numpy array, and I want to multiply it with a vector (1d array) along some dimension (which can change!). As an example, say I want to multiply a 2d array by a 1d array along axis 0 of the first array, I can do something like this: a=np.arange(20).reshape((5,4)) b=np.ones(5) c=a*b[:,np.newaxis] Easy, but I would like to extend this idea to n-dimensions (for a, while b is always 1d) and to any axis. In other