问题
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)>
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)
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
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
DataArraywith the same coordinates (lat,lon) as theDataSetfor further analysis and visualization.
The questions:
- 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)
- can i store the output directly into a
DataArrayas variables? or do i have to keep using the pandasDatraFrameand afterwards try to transform it to aDataArray?
回答1:
I believe I have the answer you are looking for.
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.
If you apply the FProphet into the u_function, then it is possible to generate an prediction output specific for each coordinate Point.
Here is a reproducible example:
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)
来源：https://stackoverflow.com/questions/56626011/using-prophet-on-netcdf-file-using-xarray