Concatenate arrays python without numpy

Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am creating inside a for loop in each iteration of it a numpy array of size 20x30x30x3. I want to concatenate all of those numpy arrays into a bigger one.

If the iteration steps are then the numpy array I want should be x30x30x3. I tried to do with lists:. How can I have x30x30x3 in the end in a numpy array?

In order to create the concatenation and work around the error, I initialized the array with None and tested if it is None in the loop. Thereby you do not have to worry about not fitting dimensions. However, i created some arrays for the ones you did only describe and ended up with a final dimesion of30, 30, 3. Hope this helps for you solution.

Use np. Don't concatenate in the first iteration, it'll raise dimension error, just copy it during the first iter. For the remaining iterations keep concatenating. Learn more. Concatenate numpy array within a for loop Ask Question. Asked 2 years, 3 months ago. Active 2 years, 3 months ago. Viewed 10k times. Improve this question. Jose Ramon. Jose Ramon Jose Ramon 4, 20 20 gold badges 59 59 silver badges bronze badges.Join Stack Overflow to learn, share knowledge, and build your career.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. In Numpy, I can concatenate two arrays end-to-end with np. Is there a way to concatenate two arrays into a viewi. Would that require an np. The memory belonging to a Numpy array must be contiguous.

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If you allocated the arrays separately, they are randomly scattered in memory, and there is no way to represent them as a view Numpy array. If you know beforehand how many arrays you need, you can instead start with one big array that you allocate beforehand, and have each of the small arrays be a view to the big array e. Just initialize the array before you fill it with data. If you want you can allocate more space than needed and it will not take up more RAM because of the way numpy works.

The memory is used only once data is put into the array.

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Creating a new array from concatenating two will never finish on a dataset of any size, i. Not really elegant at all but you can get close to what you want using a tuple to store pointers to the arrays. Now I have no idea how I would use it in the case but I have done things like this before.

I had the same problem and ended up doing it reversed, after concatenating normally with copy I reassigned the original arrays to become views on the concatenated one:. The answer is based on my other answer in Reference to ndarray rows in ndarray. Learn more. Concatenate Numpy arrays without copying Ask Question. Asked 9 years, 3 months ago. Active 2 years, 11 months ago. Viewed 40k times. Improve this question. Fred Foo. Fred Foo Fred Foo k 66 66 gold badges silver badges bronze badges.

Why do you want to have a view rather then a copy? WinstonEwert: I have a long list of arrays on which I want to perform a single, global normalization. That doesn't answer the question, what's wrong with copying all those arrays? Basically, are you concerned about the cost of copying, or do you want to modify the original arrays?

WinstonEwert: the cost of copying is the problem; otherwise I could just concatenate them and replace the original arrays with views into the concatenation.Thread Rating: 1 Vote s - 1 Average 1 2 3 4 5. Thread Modes. Posts: Reputation: 0. I want to create a 2D array and assign one particular element. The second way below works. But the first way doesn't. I am curious to know why the first way does not work.

Is there any way to create a zero 2D array without numpy and without loop?

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Posts: 4, Reputation: So you have a list of references, not a list of lists. That way there is no copying being done, so you end up with an actual list of lists. Craig "Ichabod" O'Brien - xenomind. Recommended Tutorials: BBCodefunctionsclassestext adventures.

Website Find. Jan, PM landlord Wrote: So there is no way to do this by one line code unless to use numpy? The list comprehension I showed you does it in one line of code. View a Printable Version. User Panel Messages. Log Out. View private messages unread. Login to Python Forum Enter your details to login to your account:. Remember me. Don't have an account yet? Sign Up! Linear Mode. Threaded Mode.

concatenate arrays python without numpy

Thread Modes Creating 2D array without Numpy. Nov, PM Last Post : jefsummers. How to fill datetime64 field in numpy structured array? Adding data in 3D array from 2D numpy array.

Python NumPy For Your Grandma - 4.4 concatenate()

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Stack those horizontally with np. The None parameter ensures that the arrays are flattened before concatenation the gluing of arrays. Learn more. Python: Concatenate 3 arrays Ask Question. Asked 3 years, 11 months ago. Active 1 year, 8 months ago.

How To Concatenate Arrays in NumPy?

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Cyrine Abdelkafi Cyrine Abdelkafi 1 1 gold badge 1 1 silver badge 6 6 bronze badges. Active Oldest Votes. Improve this answer. Divakar Divakar k 15 15 gold badges silver badges bronze badges. Femkemilene 2 2 silver badges 13 13 bronze badges. Slickmind Slickmind 2 2 silver badges 13 13 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.

The Overflow Blog. Podcast What are the young developers into? Featured on Meta. Opt-in alpha test for a new Stacks editor. Visual design changes to the review queues.Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. The end should should be a x 31 array. The error I get is ValueError: all the input arrays must have same number of dimensions.

Which converts the 1-d array to 2-d implicitly, and thus equivalent to np. Learn more. Concat two arrays of different dimensions numpy Ask Question. Asked 3 years, 3 months ago. Active 9 months ago. Viewed 28k times. The error I get is ValueError: all the input arrays must have same number of dimensions Can someone help? Improve this question.

Trung Tran. Trung Tran Trung Tran 8, 34 34 gold badges 93 93 silver badges bronze badges. Active Oldest Votes. You can use numpy. Improve this answer. Psidom Psidom k 18 18 gold badges silver badges bronze badges. T to convert a 1d array into 2. I like your [:, None] better.

You can simply use numpy 's hstack function. MaxiMouse 2, 1 1 gold badge 12 12 silver badges 25 25 bronze badges. Darshil Shah Darshil Shah 1 1 1 bronze badge.Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. And then I want to concatenate it with another NumPy array just like we create a list of lists.

How do we create a NumPy array containing NumPy arrays? Well, the error message says it all: NumPy arrays do not have an append method.

concatenate arrays python without numpy

There's a free function numpy. This will create a new array instead of mutating M in place.

Note that using numpy. You will get better performing code if you use fixed-sized NumPy arrays. This will not create two separate arrays but will append two arrays into a single dimensional array. Sven said it all, just be very cautious because of automatic type adjustments when append is called.

I found this link while looking for something slightly different, how to start appending array objects to an empty numpy array, but tried all the solutions on this page to no avail. Then I found this question and answer: How to add a new row to an empty numpy array. I had the same issue, and I couldn't comment on Sven Marnach answer not enough rep, gosh I remember when Stackoverflow first started Then a list of 10 random numbers is created using np.

The loop stacks it 10 high. We just have to remember to remove the first empty entry. Learn more. Asked 8 years, 10 months ago. Active 3 months ago. Viewed k times. Something like [ a b c ]. Improve this question. Hari 2 2 gold badges 12 12 silver badges 20 20 bronze badges. You can create an "array of arrays" you use an object arraybut you almost definitely don't want to.

What are you trying to do? Do you just want a 2d array? Active Oldest Votes. Improve this answer. Hi when i run this i get this np. Fraz: I've added Sven's vstack idea. You know you can create the array with array [[1,2,3],[2,3,4]]right? Thus if you need to combine more than 2 arrays, vstack is more handy.

Sven Marnach Sven Marnach k gold badges silver badges bronze badges. Fraz: Have a look at numpy. I think this should be the accepted answer as it precisely answers to the point. You may use numpy.Join Stack Overflow to learn, share knowledge, and build your career. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I have two simple one-dimensional arrays in NumPy. I should be able to concatenate them using numpy. But I get this error for the code below:. The arrays you want to concatenate need to be passed in as a sequence, not as separate arguments. From the NumPy documentation :. It was trying to interpret your b as the axis parameter, which is why it complained it couldn't convert it into a scalar. All those options are equally fast for large arrays; for small ones, concatenate has a slight edge:.

The plot was created with perfplot :. The first parameter to concatenate should itself be a sequence of arrays to concatenate:. Here are more approaches for doing this by using numpy. Some more facts from the numpy docs :. Learn more. Concatenating two one-dimensional NumPy arrays Ask Question.

Asked 8 years, 11 months ago. Active 3 months ago.

concatenate arrays python without numpy

Viewed k times. Improve this question. If you want to concatenate them into a single array along an axis, use np. If you want to stack them vertically, use np. If you want to stack them into multiple arrays horizontally, use np.

If you want to stack them depth-wise, i. Note that the latter are similar to pandas pd. Active Oldest Votes. The line should be: numpy. From the NumPy documentation : numpy. Improve this answer. Winston Ewert Winston Ewert 40k 10 10 gold badges 62 62 silver badges 79 79 bronze badges. The function is more useful in taking a sequence then if it just took two arrays. WinstonEwert Assuming the issue isn't that it's hardcoded to two arguments, you could use it like numpy. Python's fluid enough that the difference ends up feeling more cosmetic than substantial, but it's good when the API is consistent e.

Aug 24 '16 at What would happen to the axis parameter? Assuming the things to concatenate are all positional parameters, you could keep axis as a keyword argument e. It's not ideal since you can't seem to name the keyword args explicitly in the signature this way, but there are workarounds. There are several possibilities for concatenating 1D arrays, e. The alternatives all use np. They just massage the input list in various ways before hand.

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