NetCDF to CSV

Convert MARIS standard NetCDF4 files into CSV files for the legacy SQL import pipeline.

Each step is a single-responsibility function that transforms a dict of DataFrames keyed by sample group. They are composed in to_csv() below.

Read NetCDF groups

Open a standardised MARIS NetCDF file, extract each group’s variable arrays, and return them as {group_name: DataFrame}.

source

read_nc_grps


def read_nc_grps(
    fname, # Path to netcdf file
):

Read a MARIS NetCDF file and return {group: DataFrame} dict.

fname_in = Path('files/nc/100_HELCOM_MORS_2024.nc')
dfs = read_nc_grps(fname_in)
print('groups: ', list(dfs.keys()), '\n')
print('A single row: ', dfs['BIOTA'].sample(1).T)
groups:  ['BIOTA', 'SEAWATER', 'SEDIMENT'] 

A single row:                              6
SMP_ID_PROVIDER  BCLOR1995035
LON                   18.1667
LAT                 54.916698
SMP_DEPTH                 0.0
TIME                810864000
STATION                   PL2
NUCLIDE                     4
VALUE                   104.0
UNIT                        5
UNC                      7.28
DL                          1
BIO_GROUP                   4
SPECIES                   191
BODY_PART                  52
DRYWT               60.900002
WETWT                   210.0
PERCENTWT                0.29

Filter columns

Keep only columns in the CSV schema. The NetCDF has internal columns (like SMP_ID) not part of the CSV output.

source

keep_csv_cols


def keep_csv_cols(
    dfs:dict, # dict of DataFrames keyed by sample group
    cols:list={'AREA': 'area', 'BODY_PART': 'bodypar_id', 'BOTTOM': 'slicedown', 'COUNT_MET': 'counmet_id', 'DL': 'detection', 'DLV': 'detection_lim', 'DRYWT': 'drywt', 'FILT': 'filtered', 'LAB': 'lab_id', 'LAT': 'latitude', 'LON': 'longitude', 'NUCLIDE': 'nuclide_id', 'PERCENTWT': 'percentwt', 'PREP_MET': 'prepmet_id', 'PROFILE_ID': 'profile_id', 'REF_ID': 'ref_id', 'SAL': 'salinity', 'SAMP_MET': 'sampmet_id', 'SAMPLE_TYPE': 'samptype_id', 'SED_TYPE': 'sedtype_id', 'SMP_DEPTH': 'sampdepth', 'SMP_ID_PROVIDER': 'samplabcode', 'SPECIES': 'species_id', 'STATION': 'station', 'TAXONDB': 'taxondb', 'TAXONDBID': 'taxondb_id', 'TAXONDBURL': 'taxondb_url', 'TAXONNAME': 'taxonname', 'TAXONRANK': 'taxonrank', 'TAXONREPNAME': 'taxonrepname', 'TEMP': 'temperatur', 'TIME': 'begperiod', 'TOP': 'sliceup', 'TOT_DEPTH': 'totdepth', 'UNC': 'uncertaint', 'UNIT': 'unit_id', 'VALUE': 'activity', 'VOL': 'volume', 'WETWT': 'wetwt'}, # columns to keep (defaults to CSV_VARS)
):

Keep only columns listed in cols.

test = {'SEAWATER': pd.DataFrame({'SMP_ID': [1], 'TIME': [1], 'VALUE': [1], 'EXTRA': [1]})}
res = keep_csv_cols(test)
test_eq(list(res['SEAWATER'].columns), ['TIME', 'VALUE'])

Decode time

NetCDF stores time as seconds since epoch. Convert to datetime.

source

decode_time


def decode_time(
    dfs:dict, # dict of DataFrames keyed by sample group
):

Decode TIME from epoch seconds to datetime.

test = {'SEAWATER': pd.DataFrame({'TIME': [1672531200]})}
decode_time(test)
test_eq(test['SEAWATER']['TIME'].iloc[0], pd.Timestamp('2023-01-01'))

Add sample type

SQL import expects a sample type column. Each group has a fixed identifier.

source

add_sample_type


def add_sample_type(
    dfs:dict, # dict of DataFrames keyed by sample group
):

Add SAMPLE_TYPE column using group ID mapping.

test = {'SEAWATER': pd.DataFrame({'VALUE': [1]}), 'BIOTA': pd.DataFrame({'VALUE': [2]})}
add_sample_type(test)
test_eq(test['SEAWATER']['SAMPLE_TYPE'].iloc[0], 1)
test_eq(test['BIOTA']['SAMPLE_TYPE'].iloc[0], 2)

Add reference ID

Optional column from Zotero / INIS archive location. Omitted if not provided.

source

add_ref_id


def add_ref_id(
    dfs:dict, # dict of DataFrames keyed by sample group
    ref_id:int=None, # Reference ID to add as REF_ID column
):

Add REF_ID column if ref_id is provided.

test = {'SEAWATER': pd.DataFrame({'VALUE': [1]})}
add_ref_id(test)
test_eq('REF_ID' in test['SEAWATER'].columns, False)
test = {'SEAWATER': pd.DataFrame({'VALUE': [1]})}
add_ref_id(test, ref_id=42)
test_eq(test['SEAWATER']['REF_ID'].iloc[0], 42)

Add taxon information

Map BIOTA species IDs to scientific names and database references via the MARIS species lookup table.

source

get_taxon_cols


def get_taxon_cols(
    
)->dict: # {col_name: {species_id: value}} mapping

Read species lookup table, return {col_name: {species_id: value}} dict.

Exported source 
TAXON_COLS = {
    'Taxonname': 'TAXONNAME',
    'Taxonrank': 'TAXONRANK',
    'TaxonDB': 'TAXONDB',
    'TaxonDBID': 'TAXONDBID',
    'TaxonDBURL': 'TAXONDBURL',
}

source

add_taxon_info


def add_taxon_info(
    dfs:dict, # dict of DataFrames keyed by sample group
):

Add taxon columns to BIOTA from species lookup.

test = {'BIOTA': pd.DataFrame({'SPECIES': [99, 96]})}
add_taxon_info(test)
test_eq(test['BIOTA']['TAXONNAME'].tolist(), ['Gadus morhua', 'Fucus vesiculosus'])
test_eq(test['BIOTA']['TAXONRANK'].tolist(), ['species', 'species'])

Map lookup-table columns

Convert integer enum IDs to display names. DL and FILT use the Excel name column rather than the sanitised version.

source

map_lut


def map_lut(
    dfs:dict, # dict of DataFrames keyed by sample group
    cols:list, # Column names to map
    key:str='name', # LUT key column
    value:str='id', # LUT value column
    reverse:bool=True, # Reverse the mapping direction
):

Map columns using get_lut.

test = {'SEAWATER': pd.DataFrame({'DL': [1, 2, 3]})}
map_lut(test, ['DL'])
test_eq(test['SEAWATER']['DL'].tolist(), ['=', '<', 'ND'])
test = {'SEAWATER': pd.DataFrame({'FILT': [0, 1, 2]})}
map_lut(test, ['FILT'])
test_eq(test['SEAWATER']['FILT'].tolist(), ['Not available', 'Yes', 'No'])
test = {'SEAWATER': pd.DataFrame({'VALUE': [1]})}
map_lut(test, ['DL'])
test_eq(list(test['SEAWATER'].columns), ['VALUE'])

Decode remaining enumerated columns

CSV_DTYPES marks decoded vs encoded columns. DL and FILT are excluded since they use a different LUT column.

source

decode_csv_vars


def decode_csv_vars(
    dfs:dict, # dict of DataFrames keyed by sample group
):

Decode enumerated columns marked as state='decoded' in CSV_DTYPES.

NoteNote for MARIS DB team

It would be cleaner/more consistent to expect all MARIS LUT values in their encoded (integer) form during SQL import, rather than receiving a mix of decoded display names and encoded IDs.

Write CSV files

Rename columns via CSV_VARS, then write one file per group.

source

to_csv_files


def to_csv_files(
    dfs:dict, # dict of DataFrames keyed by sample group
    fname_in:str, # Input NetCDF file path
    dest_out:str=None, # Destination path stem; defaults to fname_in stem
):

Rename columns and write one CSV per group.

test = {'SEAWATER': pd.DataFrame({'TIME': [1], 'VALUE': [2]})}
fname = Path('/tmp/test_nc2csv')
to_csv_files(test, fname)
res = pd.read_csv(f'{fname}_SEAWATER.csv')
test_eq(list(res.columns), ['begperiod', 'activity'])
Path(f'{fname}_SEAWATER.csv').unlink()

Entry point

to_csv composes the helpers in order.

source

to_csv


def to_csv(
    fname_in:str, # MARIS standard NetCDF file path
    dest_out:str=None, # Destination path stem; defaults to parent of fname_in
    ref_id:int=None, # Reference ID to add as REF_ID column
):

Convert MARIS standard NetCDF file to import-ready CSV files.

Usage example

Convert a MARIS standard NetCDF file to import-ready CSV files using to_csv.

fname_in = Path('files/nc/100_HELCOM_MORS_2024.nc')
to_csv(fname_in, ref_id=100)
[Path('files/nc/100_HELCOM_MORS_2024_BIOTA.csv'),
 Path('files/nc/100_HELCOM_MORS_2024_SEAWATER.csv'),
 Path('files/nc/100_HELCOM_MORS_2024_SEDIMENT.csv')]

to_csv produces one CSV per sample type group found in the NetCDF file.

for f in sorted(Path('files/nc/').glob('100_HELCOM_MORS_2024_*.csv')): print(f.name)
100_HELCOM_MORS_2024_BIOTA.csv
100_HELCOM_MORS_2024_SEAWATER.csv
100_HELCOM_MORS_2024_SEDIMENT.csv

The output CSV includes 23 columns: sample metadata, activity, detection limit info, taxon details for biota, and reference ID. Below the first row:

df = pd.read_csv('files/nc/100_HELCOM_MORS_2024_BIOTA.csv')
print(df.head(1).T)
                                                 0
samplabcode                           BBFFG1999001
longitude                                    13.72
latitude                                     54.22
sampdepth                                      0.0
begperiod                                929404800
station                                     BGBODD
nuclide_id                                       4
activity                                     841.0
unit_id                                          4
uncertaint                                   58.87
detection                                        =
BIO_GROUP                                       11
species_id                                      96
bodypar_id                                      54
drywt                                          NaN
wetwt                                          NaN
percentwt                                   0.1692
samptype_id                                      2
ref_id                                         100
taxonname                        Fucus vesiculosus
taxonrank                                  species
taxondb                                   Wikidata
taxondb_id                                 Q754755
taxondb_url  https://www.wikidata.org/wiki/Q754755