Python: Inserting an element into an array of different size

Question

I have a numpy array like this:

[[[287  26]]

 [[286  27]]

 [[285  27]]

 ...

 [[290  27]]

 [[289  26]]

 [[288  26]]]

and I would like to insert an integer and make it an array like

[
[287  26 integer]
[286  27 integer]
.......]

however, since the first array has different size than what I want at the end, simply using insert() function did not work for me.

Is there a work around?

Thanks in advance.

EDIT: So the closest I came so far is the following:

outline_poses = []  # final array
 for cnt in cnts: # loop over each element
        outline_poses.append(cnt[0]) 
        outline_poses.append(SENSOR_MEASURED_HEIGHT) #Append this integer

Output:

[array([287,  26], dtype=int32), 60, array([286,  27], dtype=int32), 60,....]

How can I organize this array and make it look like [287, 26, 60],...?

Make a target array of the right size, and copy values to it. — hpaulj
– hpaulj, Commented Dec 3, 2018 at 11:28

Tim Maier · Accepted Answer · 2018-12-03 11:42:01Z

1

If I understand your problem right, you could use a list comprehension.

newList = np.array([np.append(x[0],integer) for x in myList])

edited Dec 3, 2018 at 11:42

answered Dec 3, 2018 at 10:53

Tim Maier

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7 Comments

Schütze Over a year ago

what is x here? I get myList but x is unclear.

Tim Maier Over a year ago

x is a local iterating variable. It iterates over each element in your list myList. Since each Element is a list of one list itself the comprehension takes the first element of the sublist and adds the list [integer]. For clearer understanding of the code you can try print [x for x in myList]

Schütze Over a year ago

Hmm I get the output of array([169, 335]), array([168, 334]), array([167, 334]), array([166, 334]), array([165, 334]), array([164, 334])], I don't think this is what I wanted.

Tim Maier Over a year ago

So you can't save your data as a normal list of lists? I assume you use numpy array. That's where the error comes from I guess.

Tim Maier Over a year ago

okay i'm no numpy geek but one last try: newList = np.array([np.append(x[0],integer) for x in myList])

|

TrebledJ · Accepted Answer · 2018-12-03 10:52:04Z

This is a three-dimensional list you have right here...

>>> myList = [[[287,  26]],
 [[286,  27]],
 [[285,  27]],
 [[290,  27]],
 [[289,  26]],
 [[288,  26]]]

...so you'll need to access your list with two-levels of depth before inserting or appending elements into the deepest lists.

>>> myList[0][0].append(42)
>>> myList[5][0].append(42)
>>> myList
[[[287, 26, 42]],
 [[286, 27]], 
 [[285, 27]], 
 [[290, 27]], 
 [[289, 26]], 
 [[288, 26, 42]]]

What happens when you insert or append elements with shallower depths? 🤔

Appending at Depth 0

>>> myList.append('Catapult')
>>> myList
[[[287, 26, 42], 'Trebuchet'],
 [[286, 27]], 
 [[285, 27]], 
 [[290, 27]], 
 [[289, 26]], 
 [[288, 26, 42]],
 'Catapult']

Appending at Depth 1

>>> myList[0].append('Trebuchet')
>>> myList[3].append('Treebuchet')
>>> myList
[[[287, 26, 42], 'Trebuchet'],
 [[286, 27]], 
 [[285, 27]], 
 [[290, 27], 'Treebuchet'], 
 [[289, 26]], 
 [[288, 26, 42]]]

Mitiku · Accepted Answer · 2018-12-03 11:41:41Z

0

If I'm correct you are trying to insert an integer to all inner lists. You can use numpy concatenate method to achieve this.

integer_to_insert = 6
original_array = np.array([[[290,  27]],[[289,  26]],[[288,  26]]])
concat_integer = np.array([integer_to_insert]* original_array.shape[0]).reshape(original_array.shape[0], 1,1) 
# This is correct if you are inserting the same integer to all lists. But as long as length of this array is equal to length of original list this array can be replaced.

concatenated = np.concatenate([original_array, concat_integer], 2)
print(concatenated)
# array([[[290,  27,   6]],
# [[289,  26,   6]],
# [[288,  26,   6]]])

edited Dec 3, 2018 at 11:41

answered Dec 3, 2018 at 11:36

Mitiku

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