slice

问题 I always thought that omitting arguments in the python slice operation would result into: start = 0 end = len(lst) step = 1 That holds true if the step is positive, but as soon as the step is negative, like in the "reverse slice" [::-1] , omitting start/end results in: start = len(lst)-1 end = None Is this a special case, or am I missing something? 回答1: The default is always None ; it is up to the type to determine how to handle None for any of the 3 values. The list object is simply passed a

问题 I would like to upload large files, using Uint8Array and slice() function. The slice() is needed, because large files have to be handled too. var fileReader = new FileReader(); fileReader.onloadend = function(event) { var contents = new Uint8Array(event.target.result); var bufferSize = 8192; var byteBuffer = []; var temp = null; var pos = 0; for(var i = 0; i < contents.length; i+=bufferSize) { pos = contents.length > i+bufferSize ? i+bufferSize : contents.length; byteBuffer.push(String

问题 I ran afoul of Swift Slice, thinking that firstIndex should be the first index of the slice, in the domain of the source (not sure what else it's useful for). Evidently this is not the case: let ary = map(1...100) { i in i } let s:Slice<Int> = ary[10..<20] s.startIndex // 0 ary[10..<20].startIndex // 0 (10..<20).startIndex // 10 (half-open interval generated from a range, presumably) Does this seem like a bug? If it's always 0, it seems totally useless. 回答1: If you dig around in the auto

问题 So this is the simplified version of the data file: Wichita, KS[3769,9734]279835 308 1002 1270 1068 1344 1360 1220 944 1192 748 1618 1774 416 1054 Wheeling, WV[4007,8072]43070 1017 1247 269 255 1513 327 589 203 1311 416 627 605 2442 998 85 West Palm Beach, FL[2672,8005]63305 1167 1550 1432 965 1249 2375 1160 718 1048 2175 760 1515 1459 3280 1794 1252 Wenatchee, WA[4742,12032]17257 3250 2390 1783 1948 2487 2595 1009 2697 2904 2589 1394 2690 1765 2912 117 1461 2358 Weed, CA[4142,12239]2879 622

问题 I want to find the first 3 elements in list by using my_list[:3] , but I cannot guarantee that the list will be at least length 3. I can only find examples with given list and small stop. So, I want to know whether my_list[:3] is acceptable without checking the length of list. Thanks! I have tried by myself and it works well. But I want to see whether any description of doc. 回答1: Given: >>> li=[1,2,3] There are really only two cases to consider. 1) If a slice that extends beyond the end of

问题 I would like to use a numpy array to build folds for a k-folds cross validation task. Taking out the test slice is easy, but I can't figure out how to return the remainder of the array, with the test slice omitted. Is there an efficient way to do this? examples = range(50) classes = range(50) data = np.array(zip(classes,examples)) test_slice = data[5:10] train_on_remainder = ?? 回答1: You could set it up like so: test_slice, remainder = np.split(data.copy(), [test_size], axis=0) # run test

问题 I have a numpy.array , called grid , with shape: grid.shape = [N, M_1, M_2, ..., M_N] The values of N, M_1, M_2, ..., M_N are known only after initialization. For this example, let's say N=3 and M_1 = 20, M_2 = 17, M_3 = 9: grid = np.arange(3*20*17*9).reshape(3, 20, 17, 9) I am trying to loop over this array, as follows: for indices, val in np.ndenumerate(grid[0]): print indices _some_func_with_N_arguments(*grid[:, indices]) At the first iteration, indices = (0, 0, 0) and: grid[:, indices] #

问题 I have a list of several thousand floats that I want to be able to slice by min and max values. E.G. using: flist = [1.9842, 9.8713, 5.4325, 7.6855, 2.3493, 3.3333] (my actual list is 400,000 floats long, but the above is a working example) I want something like def listclamp(minn, maxn, nlist): such that print listclamp(3, 8, flist) should give me [3.3333, 5.4325, 7.6855] I also need to do this 10,000 to 30,000 times, so speed does count. (I have no sample code for what I've tried so far,

问题 I have something like this: <div ng-repeat="atma in abc"> <li ng-repeat="atma in abc.slice(0,3)"><span>{{$index+1}} - {{atma.weapon}} </span></li> </div> I wanted to slice these results at, each div repeat, each time being used the 3 items from index. So I would start with the first div showing the weapons ranging from 1 to 3. The second one would have elements from 4 to 6. And so on. Can I use $index or something like that on my slice? Ps.: This question came from trying my best on this

问题 I have a dataframe, with two columns and 5000 rows. like: A B 0 1 4 1 5 5 2 3 2 3 9 7 ... 5000 8 3 I want to separate the dataframe every 100 steps. So I get 50 slices. For a training, what's I want to do next is to combine the 50 slices again into a new dataframe or array or everything that I can output the data into csv file. I used the command following to separate the dataframe into slices: df_original=pd.read_csv('/data.csv') df=pd.DataFrame(df_original, columns=['A','B']) for i in range