grib_get

grib_get(fs, keys[, grouping])

Extracts the values of a set of ecCodes keys from the GRIB headers of fs in an efficient way.

Parameters

  • fs (Fieldset) – input fieldset

  • keys (list) – the ecCodes keys

  • grouping (str) – grouping mode (“field” or “key”)

Return type

list of lists

A single call to grib_get() can replace multiple calls to the other grib_get_* functions and is hence more efficient.

By default the keys will be retrieved as str, but their type can be specified by adding a modifier to their names, following the convention used by the ecCodes command line tool grib_ls where the key name is followed by a colon and then one or two characters which specify the type:

  • s=string

  • l=long

  • d=double

  • la=long array

  • da=double array

  • n=native type New in Metview version 5.14.0.

For example, the key ‘centre’ can be retrieved as a str with ‘centre’ or ‘centre:s’, or as a number with ‘centre:l’. Each GRIB key has a ‘native type’, e.g. long or string. If the type is specified as “n” then the type that is returned. The native type for the key ‘centre’ is str, so ‘centre:n’ will return a str.

The result is always a list of lists:

  • if grouping is not specified or set to ‘field’, the result will be grouped by field, containing one list per field, each of these lists containing one element per key

  • if grouping is ‘key’, the result will be grouped by key, containing one list per key, each of these lists containing one element per field.

Example

The following lines of code on a particular fieldset with 3 fields:

print(mv.grib_get(f,
      ['editionNumber', 'centre', 'level', 'step'], 'field'))
print(mv.grib_get(f,
      ['editionNumber', 'centre:l', 'level', 'step'], 'key'))

produces this output:

[['1', 'ecmf', '1000', '0'], ['1', 'ecmf', '925', '0'], ['1', 'ecmf', '850', '0']]
[['1', '1', '1'], [98.0, 98.0, 98.0], ['1000', '925', '850'], ['0', '0', '0']]
grib_get_long(fs, key)
grib_get_double(fs, key)
grib_get_string(fs, key)
grib_get_long_array(fs, key)
grib_get_double_array(fs, key)
grib_get_string_array(fs, key)

Extracts the value of an ecCode key from the GRIB headers of fs.

Parameters

  • fs (Fieldset) – input fieldset

  • key (string) – the ecCodes key

Return type

number, str or list

This group of functions is based on the similarly named ecCodes C API functions. The available ecCodes keys can be inspected in various ways:

  • in an interactive Metview session with the GRIB Examiner (right-click Examine or double-click on a GRIB icon)

  • with the ecCodes command line tool grib_dump

Fot further details about keys read GRIB Keys - ecCodes GRIB FAQ.

grib_get_long(), grib_get_double() and grib_get_string() return a value if fs has a single field, otherwise they return a list.

grib_get_long_array() and grib_get_double_array() return a 1d-ndarray if fs has a single field, otherwise they return a list 1d-ndarrays.

grib_get_string() returns a list of strings if fs has a single field, otherwise it returns a list lists.

Note

grib_get_long() and grib_get_long_array() extract a C long value internally but it is cast into float on return.

Example

This code:

import metview as mv
print(mv.grib_get_long(data, "editionNumber"))
print(mv.grib_get_long(data, "max"))
print(mv.grib_get_double(data, "max"))
print(mv.grib_get_string(data, "max"))
print(mv.grib_get_string(data, "typeOfGrid"))

can result in the following output for single-field GRIB file:

1
317
317.278808594
317.279
regular_ll
Example

This code shows how to obtain the list of latitudes from a reduced Gaussian grid fieldset:

import metview as mv
g = mv.read('your_data_in_gg.grb')
pl = mv.grib_get_long_array (g, 'pl')
print(len(pl))
print(pl)