If I want to a array, for example:
[
[
[6,3,4],
[5,2]
],
[
[8,5,7],
[11,3]
]
]
And I just give you a simple example. In fact, the number of array of each dimensional will be changed with different conditions. And I don't want to use multiplication of list. I want to create every element directly.
How to do it?
Thank you!
Use a mapping from your multi-dimensional index to your values. Don't use a list of lists of lists.
array_3d = {
(0,0,0): 6, (0,0,1): 3, (0,0,2): 4,
(0,1,0): 5, (0,1,1): 2,
(1,0,0): 8, (1,0,1): 5, (1,0,2): 7,
(1,1,0): 11,(1,1,1): 3
}
Now you don't have to worry about "pre-allocating" any size or or number of dimensions or anything.
array_3d[1, 0, 2].I take dictionaries all the way for such cases:
def set_3dict(dict3,x,y,z,val):
"""Set values in a 3d dictionary"""
if dict3.get(x) == None:
dict3[x] = {y: {z: val}}
elif dict3[x].get(y) == None:
dict3[x][y] = {z: val}
else:
dict3[x][y][z] = val
d={}
set_3dict(d,0,0,0,6)
set_3dict(d,0,0,1,3)
set_3dict(d,0,0,2,4)
...
In anology I have a getter
def get_3dict(dict3, x, y, z, preset=None):
"""Read values from 3d dictionary"""
if dict3.get(x, preset) == preset:
return preset
elif dict3[x].get(y, preset) == preset:
return preset
elif dict3[x][y].get(z, preset) == preset:
return preset
else: return dict3[x][y].get(z)
>>> get3_dict(d,0,0,0)
6
>>> d[0][0][0]
6
>>> get3_dict(d,-1,-1,-1)
None
>>> d[-1][-1][-1]
KeyError: -1
In my opinion the advantage lies in iterating over the field being quite simple:
for x in d.keys():
for y in d[x].keys():
for z in d[x][y].keys():
print d[x][y][z]
Um, pretty much the way you'd think. In Python they're called lists, not arrays, but you just have a triple-nested list, like,
threeDList = [[[]]]
and then you use three indices to identify elements, like
threeDList[0][0].append(1)
threeDList[0][0].append(2)
#threeDList == [[[1,2]]]
threeDList[0][0][1] = 3
#threeDList == [[[1,3]]]
You just have to be careful that every index you use refers to a place in the list that already exists (i.e. threeDList[0][0][2] or threeDList[0][1] or threeDList[1] does not exist in this example), and when possible, just use comprehensions or for loops to manipulate the elements of the list.
Hope this helps!
threeDList[0][0] containing five elements, threeDList[0][1] containing seventeen, threeDList[4] containing none; it's not a definition of a cubic array.
lists, not arrays.multi-dimensional-arrayandpython. It's got some useful things there. (Suggesting numpy, for example.)