--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xarray_netcdf2netcdf.py	Sun Jun 06 08:50:43 2021 +0000
@@ -0,0 +1,133 @@
+#!/usr/bin/env python3
+#
+#  Apply operations on selected variables
+# - scale
+# one can also select the range of time (for timeseries)
+# to apply these operations over the range only
+# when a range of time is selected and when scaling, one
+# can choose to save the entire timeseries or
+# the selected range only.
+# when scaling, one can add additional filters on dimensions
+# (typically used to filter over latitudes and longitudes)
+
+
+import argparse
+import warnings
+
+import xarray as xr  # noqa: E402
+
+
+class netCDF2netCDF ():
+    def __init__(self, infile, varname, scale="",
+                 output="output.netcdf",
+                 write_all=False,
+                 filter_list="",
+                 verbose=False):
+        self.infile = infile
+        self.verbose = verbose
+        self.varname = varname
+        self.write_all = write_all
+        self.filter = filter_list
+        self.selection = {}
+        if scale == "" or scale is None:
+            self.scale = 1
+        else:
+            self.scale = float(scale)
+        if output is None:
+            self.output = "output.netcdf"
+        else:
+            self.output = output
+        # initialization
+        self.dset = None
+        self.subset = None
+        if self.verbose:
+            print("infile: ", self.infile)
+            print("varname: ", self.varname)
+            print("filter_list: ", self.filter)
+            print("scale: ", self.scale)
+            print("write_all: ", self.write_all)
+            print("output: ", self.output)
+
+    def dimension_selection(self, single_filter):
+        split_filter = single_filter.split('#')
+        dimension_varname = split_filter[0]
+        op = split_filter[1]
+        ll = int(split_filter[2])
+        if (op == 'sl'):
+            rl = int(split_filter[3])
+            self.selection[dimension_varname] = slice(ll, rl)
+        elif (op == 'to'):
+            self.selection[dimension_varname] = slice(None, ll)
+        elif (op == 'from'):
+            self.selection[dimension_varname] = slice(ll, None)
+        elif (op == 'is'):
+            self.selection[dimension_varname] = ll
+
+    def filter_selection(self):
+        for single_filter in self.filter:
+            self.dimension_selection(single_filter)
+        if self.write_all:
+            self.ds[self.varname] = \
+                self.ds[self.varname].isel(self.selection)*self.scale
+        else:
+            self.dset = \
+                self.ds[self.varname].isel(self.selection)*self.scale
+
+    def compute(self):
+        if self.dset is None:
+            self.ds = xr.open_dataset(self.infile)
+            if self.filter:
+                self.filter_selection()
+                if self.verbose:
+                    print(self.selection)
+            elif self.write_all is not None:
+                self.dset = self.ds[self.varname]
+
+    def save(self):
+        if self.write_all:
+            self.ds.to_netcdf(self.output)
+        else:
+            self.dset.to_netcdf(self.output)
+
+
+if __name__ == '__main__':
+    warnings.filterwarnings("ignore")
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        'input',
+        help='input filename in netCDF format'
+    )
+    parser.add_argument(
+        'varname',
+        help='Specify which variable to plot (case sensitive)'
+    )
+    parser.add_argument(
+        '--filter',
+        nargs="*",
+        help='Filter list variable#operator#value_s#value_e'
+    )
+    parser.add_argument(
+        '--output',
+        help='Output filename to store the resulting netCDF file'
+    )
+    parser.add_argument(
+        '--scale',
+        help='scale factor to apply to selection (float)'
+    )
+    parser.add_argument(
+        "--write_all",
+        help="write all data to netCDF",
+        action="store_true")
+    parser.add_argument(
+        "-v", "--verbose",
+        help="switch on verbose mode",
+        action="store_true")
+    args = parser.parse_args()
+
+    dset = netCDF2netCDF(infile=args.input, varname=args.varname,
+                         scale=args.scale, output=args.output,
+                         filter_list=args.filter,
+                         write_all=args.write_all,
+                         verbose=args.verbose)
+    dset.compute()
+    dset.save()