Question

得到一个包含几列的csv文件，并且数据包含某些列的空值。使用pandas dataframe函数，如何将包含空值和空列名的列总数打印到输出的csv文件中？

Output.csv 2＃列数列a b列

Answer 1

尝试：

import UIKit

class ViewController: UIViewController {

    private lazy var cameraService = CameraService()
    private weak var button: UIButton?
    private weak var imagePreviewView: UIImageView?
    private var cameraInited = false

    private enum ButtonState { case cancel, makeSnapshot }
    private var buttonState = ButtonState.makeSnapshot {
        didSet {
            switch buttonState {
                case .makeSnapshot: button?.setTitle("Make a photo", for: .normal)
                case .cancel: button?.setTitle("Cancel", for: .normal)
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        setupCameraPreviewView()
        setupButton()
        // Do any additional setup after loading the view.
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        cameraService.start()
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        cameraService.stop()
    }

    // Ensure that the interface stays locked in Portrait.
    override var supportedInterfaceOrientations: UIInterfaceOrientationMask {
        return .portrait
    }

    // Ensure that the interface stays locked in Portrait.
    override var preferredInterfaceOrientationForPresentation: UIInterfaceOrientation {
        return .portrait
    }
}


extension ViewController {

    private func setupCameraPreviewView() {
        let previewView = UIView(frame: .zero)
        view.addSubview(previewView)
        previewView.translatesAutoresizingMaskIntoConstraints = false
        previewView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        previewView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        previewView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        previewView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        previewView.layoutIfNeeded()
        cameraService.prepare(previewView: previewView, cameraPosition: .front) { [weak self] success in
            if success { self?.cameraService.start() }
        }
    }

    private func setupButton() {
        let button = UIButton(frame: .zero)
        button.addTarget(self, action: #selector(buttonTouchedUpInside), for: .touchUpInside)
        view.addSubview(button)
        self.button = button
        buttonState = .makeSnapshot
        button.translatesAutoresizingMaskIntoConstraints = false
        button.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        button.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        button.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        button.heightAnchor.constraint(equalToConstant: 44).isActive = true
        button.backgroundColor = UIColor.black.withAlphaComponent(0.4)
    }

    private func show(image: UIImage) {
        let imageView = UIImageView(frame: .zero)
        view.insertSubview(imageView, at: 1)
        imagePreviewView = imageView
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        imageView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
        imageView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
        imageView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        imageView.image = image
    }

    @objc func buttonTouchedUpInside() {
        switch buttonState {
        case .makeSnapshot:
            cameraService.capturePhoto { [weak self] image in
                guard let self = self else {return }
                self.cameraService.stop()
                self.buttonState = .cancel
                self.show(image: image)
            }
        case .cancel:
            buttonState = .makeSnapshot
            cameraService.start()
            imagePreviewView?.removeFromSuperview()
        }
    }
}

其中a是您的数据帧名称，并且要检查整个列是否为空，将any（）更改为all（）。

Answer 2

以下代码可帮助您达到上述要求：

    df=pd.DataFrame({'Name':["abc","def",None],'Age':[1,None,3],'Address':["rst","uvw","xyz"]})

    null_colname=df.columns[df.isnull().any()].tolist() #find columns which returns True for null testing and convert the column names to list
    null_colnum=len(null_colname)                       # take length of the above list

    p=str(null_colnum)+"# of columns:"                  # initialize string in the format of required output
    for i in range(0,null_colnum):                      #iterate over the list
        p=p+'Column-'+null_colname[i]+' '               # concatenate column names to the string


    text_file = open(filepath+"Output.csv", "w")        #export to csv
    text_file.write("%s" % p)
    text_file.close()

Answer 3

我准备了如下测试数据：

np.random.seed(0)
df = pd.DataFrame(np.random.random(size=(5, 10)), columns=list('ABCDEFGHIJ'))
df[df > 0.9] = pd.np.nan; df

要获取包含名称 NaN 的列名，请运行：

nn = df.isnull().any()

对于我的测试数据，结果是：

A     True
B    False
C    False
D     True
E    False
F    False
G    False
H     True
I     True
J    False
dtype: bool

我们实际上对索引值为 True 的索引值感兴趣。要获取它们，请运行：

nullCols = nn.index[nn].tolist()

结果是：

['A', 'D', 'H', 'I']

要获取此类列的数量，请运行：

len(nullCols)

结果为4。

在python中如何打印包含空值的列总数以及如何将null的列名打印到csv输出文件

3 个答案: