Numpy - 总结一个向量列表

Question

我想在列表中总结NumPy向量列表。 （在这个例子中，它是一个包含2个项目的列表，但在我的情况下，列表可以是任何大小。）如何将它们加到一个新的向量中？

<table  class="table table-datatable table-bordered" id="tableID">
    <thead>
        <tr>
            <th class="nosort"><input type="checkbox" id="checkAllreInvitation" /></th>
            <th class="sort-alpha">Employee name</th>
            <th class="sort-alpha">Send Date</th>
            <th class="sort-alpha">Sender</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td><input type="checkbox" name="userUid[]" value="{user.uid}" id="checkAllreInvitation" class="checkItemre validate[required]" /></td>
            <td>Alexander Schwartz</td>
            <td>27.12.2015</td>
            <td>dummy@email.com</td>
        </tr>
    </tbody>
</table>
<script type="text/javascript">
    $(document).ready(function() {
        $('#tableID').DataTable({
            'iDisplayLength':100,
            "aaSorting": [[ 0, "asc" ]],
            'aoColumnDefs': [{
                'bSortable': false,
                'aTargets': ['nosort']
            }]
        });
    });
</script>

a = np.array([100, 100]) b = np.array([200, 200]) my_list = [a, b] ab = np.add(my_list) 有效，但不是列表。我已经尝试了np.add(a, b)和np.add(*my_list)以及np.add(np.array(my_list))，但没有成功。这样做的正确方法是什么？谢谢！

Answer 1

解决方案1 ​​np.add.reduce()

您可以使用reduce的{​​{1}}属性：

np.add

结果：

a = np.array([100, 100])
b = np.array([200, 200])
c = np.array([1000, 2000])
L = [a, b, c]
np.add.reduce(L)

所有带有两个参数的通用函数都有一个array([1300, 2300]) 属性，它适用于reduce这个函数，即：

reduce

变为：

np.add.reduce(L)

如果列表np.add(np.add(L[0], L[1]), L[2]) 变大，请添加更多括号和相应的np.add调用。

来自文档：

  

文档字符串：

L

     

通过沿一个轴应用ufunc，将 reduce(a, axis=0, dtype=None, out=None, keepdims=False) 的维度减一。

解决方案2 a

或者，您可以沿第一轴使用np.sum()：

np.sum

效果

两者的表现似乎都是一样的。

对于小型阵列：

>>> np.sum(L, axis=0)
array([1300, 2300

a = np.array([100, 100]) b = np.array([200, 200]) c = np.array([1000, 2000]) L = [a, b, c, a, b, c, a, b, c] 加快了一点：

reduce

对于大型阵列：

%timeit np.sum(L, axis=0)

10000 loops, best of 3: 20.7 µs per loop

%timeit np.add.reduce(L)
100000 loops, best of 3: 15.7 µs per loop

没有区别：

size = int(1e6)
a = np.random.random(size)
b = np.random.random(size)
c = np.random.random(size)
L = [a, b, c, a, b, c, a, b, c]

Answer 2

这是你的意思吗？

import numpy as np

a = np.array([100, 100])
b = np.array([200, 200])
my_list = [a, b]

# add them up "vertically"

print np.vstack(my_list).sum(axis=0)

print np.vstack(tuple(my_list)).sum(axis=0)  # I thought it had to be a tuple but apparently not!


[300 300]
[300 300]

Answer 3

您可以使用import UIKit class ViewController: UIViewController,UIImagePickerControllerDelegate,UINavigationControllerDelegate { @IBOutlet weak var myImageView: UIImageView! @IBOutlet weak var myImageVie2: UIImageView! let picker = UIImagePickerController() func noCamera(){ let alertVC = UIAlertController(title: "No Camera",message: "Sorry, this device has no camera",preferredStyle: .Alert) let okAction = UIAlertAction(title: "OK",style:.Default,handler: nil) alertVC.addAction(okAction) presentViewController(alertVC,animated: true,completion: nil) } @IBAction func photoFromLibrary(sender: UIBarButtonItem) { picker.allowsEditing = false //2 picker.sourceType = .PhotoLibrary //3 picker.modalPresentationStyle = .Popover presentViewController(picker,animated: true,completion: nil)//4 picker.popoverPresentationController?.barButtonItem = sender } //take a picture, check if we have a camera first. @IBAction func shootPhoto(sender: UIBarButtonItem) { if UIImagePickerController.availableCaptureModesForCameraDevice(.Rear) != nil { picker.allowsEditing = false picker.sourceType = UIImagePickerControllerSourceType.Camera picker.cameraCaptureMode = .Photo picker.modalPresentationStyle = .FullScreen presentViewController(picker,animated: true,completion: nil) } else { noCamera() } } override func viewDidLoad() { super.viewDidLoad() picker.delegate = self func imagePickerController(picker: UIImagePickerController,didFinishPickingMediaWithInfo info: [String : AnyObject]) { var chosenImage = info[UIImagePickerControllerOriginalImage] as! UIImage myImageView.contentMode = .ScaleAspectFit myImageView.image = chosenImage UIImageWriteToSavedPhotosAlbum(chosenImage, nil, nil, nil); dismissViewControllerAnimated(true, completion: nil) } func imagePickerControllerDidCancel(picker: UIImagePickerController) { dismissViewControllerAnimated(true,completion: nil)} } 或np.hstack：

np.concatenate

Answer 4

可能是减少的理想候选人

>>> a = np.array([100, 100])
>>> b = np.array([200, 200])
>>> c = np.array([300, 300])
>>> reduce(lambda x,y: np.add(x,y), [a,b,c])
array([600, 600])