使用xarray在netCDF文件上使用先知

问题描述

我有一个用xarray读取的'netCDF'文件，我想用它为文件中的每个像素生成一个预测.

I have a 'netCDF' file which I have read with xarray and I want to use to generate a forecast for each pixel in the file.

import xarray as xr
from fbprophet import Prophet
import time

with xr.open_dataset('avi.nc',
                     chunks={'y': 2, 'x':2}) as avi:
    print(avi)

<xarray.Dataset>
Dimensions:  (ds: 104, lat: 213, lon: 177)
Coordinates:
  * lat      (lat) float64 -2.711e+06 -2.711e+06 -2.711e+06 -2.711e+06 ...
  * lon      (lon) float64 1.923e+06 1.924e+06 1.924e+06 1.924e+06 1.924e+06 ...
  * ds       (ds) object '1999-07-16T23:46:04.500000000' ...
Data variables:
    y        (ds, lat, lon) float64 dask.array<shape=(104, 213, 177),
        chunksize=(104, 2, 2)>

我为每个像素创建模型的方式是:*遍历数组(for i in range(dataset.sizes['lat']):)中的每个像素，*创建模型(m1)，*将模型输出发送到pandas DataFrame(output)

The way I'm creating the model for each pixel is by:* looping through each pixel in the array (for i in range(dataset.sizes['lat']):),* creating the model (m1),* send the model output to a pandas DataFrame (output)

我已经尝试过分块" netCDF文件，但是我发现效率没有区别.下面是我目前使用的代码.

i've tried 'chunking' the netCDF file, but i see no difference in the efficiency.Below is the code im using at the moment.

columns = ('Year','lat', 'lon')
dates = list(range(1996, 1999))
output = pd.DataFrame(columns=columns)
forecast2 = pd.DataFrame()

def GAM2 (dataset):
    for i in range(dataset.sizes['lat']):
        for k in range(dataset.sizes['lon']):
            count +=1
            df1 = dataset.y.isel(lat=slice(px_lat, (px_lat+1)), lon=slice(px_lon, (px_lon+1))).to_dataframe()

            df1['ds'] = pd.to_datetime(df1.index.get_level_values(0), dayfirst=True)
            df1['doy'] = df1['ds'].dt.dayofyear

            m1 = Prophet(weekly_seasonality=False).fit(df1)
            future1 = m1.make_future_dataframe()
            output _data = {
                    'Year': year,
                    'lat': dataset.lat[px_lat].values,
                    'lon': dataset.lon[px_lon].values}

            output = output .append(output , ignore_index=True)
            if px_lon < (dataset.sizes['lon'] - 1):
                px_lon += 1
            else:
                px_lon = 0
        if px_lat < dataset.sizes['lat']:
            px_lat += 1
        else:
            px_lat = 0

    return output

问题:

• 我正在手动遍历数组(即for i in range(dataset.sizes['lat']): ....
• 当前输出将输出到pandas数据框，我需要它转到与DataSet具有相同坐标(lat，lon)的DataArray进行进一步的分析和可视化.

The problems:

• I'm mannually looping through the array (i.e. for i in range(dataset.sizes['lat']): ....
• The output is currently going to a pandas dataframe and i need it to go to a DataArray with the same coordinates (lat, lon) as the DataSetfor further analysis and visualization.
• dataset.apply()是否可以使用此类功能?例如:
• does dataset.apply() work with these kind of functions? for example:

def GAM2 (dataset, index_name, site_name):
            m1 = Prophet(weekly_seasonality=False).fit(df1)
            future1 = m1.make_future_dataframe()
            output _data = {
                    'Year': year,
                    'lat': dataset.lat[px_lat].values,
                    'lon': dataset.lon[px_lon].values}
    return output

ds.apply(GAM2)

• 我可以将输出直接存储为DataArray作为变量吗?还是我必须继续使用熊猫DatraFrame然后将其转换为DataArray?
• can i store the output directly into a DataArray as variables? or do i have to keep using the pandas DatraFrame and afterwards try to transform it to a DataArray?

推荐答案

我相信您正在寻找答案.

I believe I have the answer you are looking for.

您可以使用xarray的矢量化u_function来实现并行计算，而不必在xarray DataArray的每个坐标点上进行双循环.

Instead of doing a double loop over each of the coordinate Points of the xarray DataArray, one can use the vectorized u_function of the xarray which allows parallel computing.

如果将FProphet应用于u_function，则可以生成特定于每个坐标点的预测输出.

If you apply the FProphet into the u_function, then it is possible to generate an prediction output specific for each coordinate Point.

以下是可重现的示例:

import pandas as pd
pd.set_option('display.width', 50000)
pd.set_option('display.max_rows', 50000)
pd.set_option('display.max_columns', 5000)


import numpy as np
import xarray as xr

from dask.diagnostics import ProgressBar
from fbprophet import Prophet

# https://stackoverflow.com/questions/56626011/using-prophet-on-netcdf-file-using-xarray

 #https://gist.github.com/scottyhq/8daa7290298c9edf2ef1eb05dc3b6c60
ds = xr.tutorial.open_dataset('rasm').load()

def parse_datetime(time):
    return pd.to_datetime([str(x) for x in time])

ds.coords['time'] = parse_datetime(ds.coords['time'].values)


ds = ds.isel({'x':slice(175,180), 'y':slice(160,170)})
ds.isel({'time':0}).Tair.plot()

ds = ds.chunk({'x':40, 'y':40})

def fillna_in_array(x):
    y = np.where(np.abs(x)==np.inf, 0, x)

    y = np.where(np.isnan(y), 0, y)

    if np.all(y) == 0:

        y = np.arange(len(y))
    return y



def xarray_Prophet(y, time, periods=30, freq='D'):
    '''
    This is a vectorized u_function of the Prophet prediction module.

    It returns an array of values containing original and predicted values
    according to the provided temporal sequence.

    Parameters:

        y (array): an array containing the y past values that will be
                   used for the prediction.

        time (array): an array containing the time intervals of each respective
                      entrance of the sampled y

        periods (positive int): the number of times it will be used for prediction

        freq (str): the frequency that will be used in the prediction:
            (i.e.: 'D', 'M', 'Y', 'm', 'H'...)

    Returns:

        array of predicted values of y (yhat)

    '''


    # Here, we ensure that all data is filled. Since Xarray has some Issues with
    # sparse matrices, It is a good solution for all NaN, inf, or 0 values for
    # sampled y data

    with ProgressBar():
        y = fillna_in_array(y)

        # here the processing really starts:

        forecast = pd.DataFrame()

        forecast['ds'] = pd.to_datetime(time)
        forecast['y'] = y


        m1 = Prophet(weekly_seasonality=True,
                     daily_seasonality=False).fit(forecast)

        forecast = m1.make_future_dataframe(periods=periods, freq=freq)

        # In here, the u_function should return a simple 1-D array,
        # or a pandas  series.
        # Therefore, we select the attribute 'yat' from the
        # FProphet prediction dataframe to return solely a 1D data.

    return m1.predict(forecast)['yhat']

def predict_y(ds,
              dim=['time'],
              dask='allowed',
              new_dim_name=['predicted'],
              periods=30, freq='D'):

    '''
    Function Description:

        This function is a vectorized parallelized wrapper of
        the "xarray_Prophet".

        It returns a new Xarray object (dataarray or Dataset) with the new
        dimension attached.

    Parameters:
        ds (xarray - DataSet/DataArray)

        dim (list of strings): a list of the dimension that will be used in the
        reduction (temporal prediction)

        dask (str):  allowed

        new_dim_name (list of strings): it contains the name that will be used
                                        in the reduction operation.

        periods (positive int): the number of steps to be predicted based
                                      on the parameter "freq".


        freq (str): the frequency that will be used in the prediction:
            (i.e.: 'D', 'M', 'Y', 'm', 'H'...)



    Returns:

        Xarray object (Dataset or DataArray): the type is solely dependent on
                                              the ds object's type.

    '''
    with ProgressBar():
        ds = ds.sortby('time', False)

        time = np.unique(ds['time'].values)

        kwargs = {'time':time,
                  'periods': periods,
                  'freq':freq}


        filtered = xr.apply_ufunc(xarray_Prophet,
                                      ds,
                                      dask=dask,
                                      vectorize=True,
                                      input_core_dims=[dim],
                                      #exclude_dims = dim, # This must not be setted.
                                      output_core_dims=[new_dim_name],
                                      kwargs=kwargs,
                                      output_dtypes=[float],
                                      join='outer',
                                      dataset_fill_value=np.nan,
                                      ).compute()

    return filtered



da_binned = predict_y( ds = ds['Tair'],
                       dim = ['time'],
                       dask='allowed',
                       new_dim_name=['predicted'],
                       periods=30).rename({'predicted':'time'})



print(da_binned)

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