Printing data as a 4 column table also error

Question

I want to ask something. I'm trying to run the code shown below. But line 40, in

time_dim, lat_dim, lon_dim = t2m.get_dims ()

I get the error

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

How can I solve this. Can you help me please?

My code is below:

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

Basically, you are trying to assign the output of t2m.get_dims() into 3 variables:

• time_dim,
• lat_dim,
• lon_dim

However, in reality, the call to t2m.get_dims() returns more than 3 values.
And that's why you have the error: too many values to unpack

---

TROUBLESHOOT:

✅ Step 1 > Assign the return value to a list (outputs) > outputs = t2m.get_dims()
✅ Step 2 > Print the outputs to see the list elements > print(outputs)
✅ Step 3 > Find out which indexes correspond to which value of time_dim, lat_dim, lon_dim
✅ Step 4 > Assign the values based on the corresponding index, like: time_dim = outputs[0]

Answer 2

Thank you for the solution. It looks like it's okay. When I add code to download in CSV format, I encounter the following situation. I do not understand why this is happening. The code I added: Write data as a table with 4 columns: time, latitude, longitude, value

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