将数据打印为 4 列 table 也出错

Question

我想问一下。我正在尝试运行下面显示的代码。但是第 40 行，在

time_dim, lat_dim, lon_dim = t2m.get_dims ()

我收到错误

ValueError: too many values to unpack (expected 3).

我该如何解决这个问题。你能帮帮我吗？

我的代码如下：

import cdsapi
import netCDF4
from netCDF4 import num2date
import numpy as np
import os
import pandas as pd
 
# Retrieve data and store as netCDF4 file
c = cdsapi.Client()
file_location = 'r"C:\Users\A\Desktop\download.nc"'
c.retrieve(
    'reanalysis-era5-single-levels',
    {
        'product_type':'reanalysis',
        'variable':'2m_temperature',  # 't2m'
        'year':'2019',
        'month':'06',
        'day':[
            '24','25'
        ],
        'time':[
            '00:00','06:00','12:00',
            '18:00'
        ],
        'format':'netcdf'
    },
    file_location)
 
# Open netCDF4 file
f = netCDF4.Dataset(file_location)
 
# Extract variable
t2m = f.variables['t2m']
 
# Get dimensions assuming 3D: time, latitude, longitude
time_dim, lat_dim, lon_dim = t2m.get_dims()
time_var = f.variables[time_dim.name]
times = num2date(time_var[:], time_var.units)
latitudes = f.variables[lat_dim.name][:]
longitudes = f.variables[lon_dim.name][:]
 
output_dir = './'

Answer 1

基本上，您试图将 t2m.get_dims() 的输出分配给 3 个变量：

time_dim,
lat_dim,
lon_dim

然而，在现实中，对t2m.get_dims() return的调用超过3个值.
这就是您出现错误的原因：too many values to unpack

疑难解答：

✅ 第 1 步 > 将 return 值分配给列表（输出）> outputs = t2m.get_dims()
✅ 第 2 步 > 打印输出以查看列表元素 > print(outputs)
✅ 步骤 3 > 找出哪些索引对应于 time_dim、lat_dim、lon_dim
的哪个值 ✅ Step 4 > 根据对应的索引赋值，如：time_dim = outputs[0]

Answer 2

感谢您提供解决方案。看起来还可以。当我添加代码以CSV格式下载时，遇到如下情况。我不明白为什么会这样。我添加的代码：将数据写入具有 4 列的 table：时间、纬度、经度、值

filename = os.path.join (output_dir, 'table.csv')
print (f'Writing data in tabular form to {filename} (this may take some time) ... ')
times_grid, latitudes_grid, longitudes_grid = [
    x.flatten () for x in np.meshgrid (times, latitudes, longitudes, indexing = 'ij')]
df = pd.DataFrame ({
    'time': [t.isoformat () for t in times_grid],
    'latitude': latitudes_grid,
    'longitude': longitudes_grid,
    't2m': t2m [:]. flatten ()))
df.to_csv (filename, index = False)
print ('Done')
================================================== ==
The situation I encountered:

  File "C: \ Users \ A \ Downloads \ untitled2.py", line 61, in <module>
    df = pd.DataFrame ({

  File "C: \ Users \ A \ anaconda3 \ lib \ site-packages \ pandas \ core \ frame.py", line 435, in __init__
    mgr = init_dict (data, index, columns, dtype = dtype)

  File "C: \ Users \ A \ anaconda3 \ lib \ site-packages \ pandas \ core \ internals \ construction.py", line 254, in init_dict
    return arrays_to_mgr (arrays, data_names, index, columns, dtype = dtype)

  File "C: \ Users \ A \ anaconda3 \ lib \ site-packages \ pandas \ core \ internals \ construction.py", line 64, in arrays_to_mgr
    index = extract_index (arrays)

  File "C: \ Users \ A \ anaconda3 \ lib \ site-packages \ pandas \ core \ internals \ construction.py", line 365, in extract_index
    raise ValueError ("arrays must all be same length")

ValueError: arrays must all be same length

将数据打印为 4 列 table 也出错

Printing data as a 4 column table also error

python

era5