python - Numpy: Multidimensional index. Row by row with no loop -

-

i have nx2x2x2 array called a. have nx2 array called b, tells me position of last 2 dimensions of in interested. getting nx2 array, either using loop (as in c in code below) or using list comprehension (as in d in code below). want know whether there time gains vectorization, and, if so, how vectorize task.

my current approach vectorization (e in code below), using b index each submatrix of a, not return want. want e return same c or d.

input:

a=np.reshape(np.arange(0,32),(4,2,2,2)) print("a") print(a) b=np.concatenate((np.array([0,1,0,1])[:,np.newaxis],np.array([1,1,0,0])[:,np.newaxis]),axis=1) print("b") print(b) c=np.empty(shape=(4,2)) n in range(0, 4):     c[n,:]=a[n,:,b[n,0],b[n,1]] print("c") print(c) d = np.array([a[n,:,b[n,0],b[n,1]] n in range(0, 4)]) print("d") print(d) e=a[:,:,b[:,0],b[:,1]] print("e") print(e)

output:

a [[[[ 0  1]    [ 2  3]]    [[ 4  5]    [ 6  7]]]    [[[ 8  9]    [10 11]]    [[12 13]    [14 15]]]    [[[16 17]    [18 19]]    [[20 21]    [22 23]]]    [[[24 25]    [26 27]]    [[28 29]    [30 31]]]] b [[0 1]  [1 1]  [0 0]  [1 0]] c [[  1.   5.]  [ 11.  15.]  [ 16.  20.]  [ 26.  30.]] d [[ 1  5]  [11 15]  [16 20]  [26 30]] e [[[ 1  3  0  2]   [ 5  7  4  6]]   [[ 9 11  8 10]   [13 15 12 14]]   [[17 19 16 18]   [21 23 20 22]]   [[25 27 24 26]   [29 31 28 30]]]

the complicated slicing operation done in vectorized manner -

shp = a.shape out = a.reshape(shp[0],shp[1],-1)[np.arange(shp[0]),:,b[:,0]*shp[3] + b[:,1]]

you using first , second columns of b index third , fourth dimensions of input 4d array, a. means is, slicing 4d array, last 2 dimensions being fused together. so, need linear indices fused format using b. of course, before doing that, need reshape a 3d array a.reshape(shp[0],shp[1],-1).

verify results generic 4d array case -

in [104]: = np.random.rand(6,3,4,5)      ...: b = np.concatenate((np.random.randint(0,4,(6,1)),np.random.randint(0,5,(6,1))),1)      ...:   in [105]: c=np.empty(shape=(6,3))      ...: n in range(0, 6):      ...:     c[n,:]=a[n,:,b[n,0],b[n,1]]      ...:       in [106]: shp = a.shape      ...: out = a.reshape(shp[0],shp[1],-1)[np.arange(shp[0]),:,b[:,0]*shp[3] + b[:,1]]      ...:   in [107]: np.allclose(c,out) out[107]: true

Comments

Post a Comment

Popular posts from this blog

python - TypeError: start must be a integer -

-
i trying draw 5 turtles, getting typeerror on line 25. here code: import turtle wn = turtle.screen() redrose = turtle.turtle() color = input("what background color be?") fillcolor_f = input("what color of rose be?") redrose.hideturtle() redrose.speed(30) redrose.penup() redrose.left(180) redrose.forward(175) redrose.right(90) redrose.forward(30) redrose.right(90) redrose.pendown() def drawrose(red): redrose.color("pink") redrose.fillcolor(fillcolor_f) redrose.fill(true) in range(red): redrose.forward(i) redrose.right(49) in range(5): drawrose(redrose) redrose.penup() redrose.forward(350) redrose.right(144) redrose.pendown() redrose.fill(false) drawrose(50) wn.bgcolor(color) i trying draw 5 roses, produces errors. doing in interactivepython.org. you recursively calling drawrose wrong parameter. on line 23 ( for in range(red): ) expect red integer...
Read more

c# - DevExpress RepositoryItemComboBox BackColor property ignored -

-
i have following code almost works properly; private void cbstatus_drawitem(object sender, listboxdrawitemeventargs e) { string item = e.item string; if (item != null) { switch (item) { case "1": e.appearance.forecolor = color.green; e.appearance.backcolor = color.green; break; case "2": e.appearance.forecolor = color.orange; e.appearance.backcolor = color.orange; break; case "3": e.appearance.forecolor = color.red; e.appearance.backcolor = color.red; break; } } } when dropdown shown, items forecolor correct, backcolor remains whatever backcolor of theme is; i.e. if i've got set dark theme, backcolor dark, cells in gridview, rather being green/orange/red. i've tried setting e.appearance.options.usebackcolor trying set e....
Read more

django - Creating multiple model instances in DRF3 -

-
1) create multiple model instances 1 api call, asked here: how create multiple model instances django rest framework? tried solution named in link, no success. i trying upload multiple files in 1 api call. result: files uploaded (only once overwrote perform_create) 1 instance created (if send 2 files, latter created instance). my code: class fileuploadserializer(serializers.modelserializer): def __init__(self, *args, **kwargs): many = kwargs.pop('many', true) super(fileuploadserializer, self).__init__(many=many, *args, **kwargs) class meta: model = fileupload read_only_fields = ('created', 'datafile', 'owner') class fileuploadviewset(viewsets.modelviewset): queryset = fileupload.objects.all() serializer_class = fileuploadserializer parser_classes = (multipartparser, formparser, ) def perform_create(self, serializer): file_list = self.request.data.getlist('file') ...
Read more