extracting variables from nc file

I have cmip5 SPECIFIC HUMIDITY data for RCP 4.5.When I open it in matlab it is showing plev

end Size:       15x1
         Dimensions: plev
         Datatype:   double
         Attributes:
                     units         = 'Pa'
                     axis          = 'Z'
                     positive      = 'down'
                     long_name     = 'pressure'
                     standard_name = 'air_pressure'

there are 15 pressure level. They are 1000, 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, and 10 hPa; But I want only four pressure level 500,700,850 and 1000 pa. If there is any way in matlab to extract only four from nc file and save it in nc file again. The total ncdisplay is shown below

ncdisp('C:\Users\DELL\Downloads\hus_day_MPI-ESM-MR_rcp45_r1i1p1_20660101-20661231.nc');
Source:
           C:\Users\DELL\Downloads\hus_day_MPI-ESM-MR_rcp45_r1i1p1_20660101-20661231.nc
Format:
           classic
Global Attributes:
           institution           = 'Max Planck Institute for Meteorology'
           institute_id          = 'MPI-M'
           experiment_id         = 'rcp45'
           source                = 'MPI-ESM-MR 2011; URL:  ECHAM6 (REV: 4936), T63L47; land: JSBACH (REV: 4936); ocean: MPIOM (REV: 4936), GR15L40; sea ice: 4936; marine bgc: HAMOCC (REV: 4936);'
           model_id              = 'MPI-ESM-MR'
           forcing               = 'GHG,Oz,SD,Sl,Vl,LU'
           parent_experiment_id  = 'historical'
           parent_experiment_rip = 'r1i1p1'
           branch_time           = 5.7e+04
           contact               = '[e-mail]'
           history               = 'Model raw output postprocessing with modelling environment (IMDI) at DKRZ: URL: http://svn-mad.zmaw.de/svn/mad/Model/IMDI/trunk, REV: 3914 2011-10-12T13:23:31Z CMOR rewrote data to comply with CF standards and CMIP5 requirements.'
           references            = 'ECHAM6: n/a; JSBACH: Raddatz et al., 2007. Will the tropical land biosphere dominate the climate-carbon cycle feedback during the twenty first century? Climate Dynamics, 29, 565-574, doi 10.1007/s00382-007-0247-8;  MPIOM: Marsland et al., 2003. The Max-Planck-Institute global ocean/sea ice model with orthogonal curvilinear coordinates. Ocean Modelling, 5, 91-127;  HAMOCC: Technical Documentation, http://www.mpimet.mpg.de/fileadmin/models/MPIOM/HAMOCC5.1_TECHNICAL_REPORT.pdf;'
           initialization_method = 1
           physics_version       = 1
           tracking_id           = 'd62b75e6-f154-47b2-ab6e-633e03455be5'
           product               = 'output'
           experiment            = 'RCP4.5'
           frequency             = 'day'
           creation_date         = '2011-10-12T13:23:31Z'
           Conventions           = 'CF-1.4'
           project_id            = 'CMIP5'
           table_id              = 'Table day (27 April 2011) 86d1558d99b6ed1e7a886ab3fd717b58'
           title                 = 'MPI-ESM-MR model output prepared for CMIP5 RCP4.5'
           parent_experiment     = 'historical'
           modeling_realm        = 'atmos'
           realization           = 1
           cmor_version          = '2.6.0'
Dimensions:
           time = 365   (UNLIMITED)
           plev = 15
           lat  = 96
           lon  = 192
           bnds = 2
Variables:
    time     
           Size:       365x1
           Dimensions: time
           Datatype:   double
           Attributes:
                       bounds        = 'time_bnds'
                       units         = 'days since 1850-1-1 00:00:00'
                       calendar      = 'proleptic_gregorian'
                       axis          = 'T'
                       long_name     = 'time'
                       standard_name = 'time'
    time_bnds
           Size:       2x365
           Dimensions: bnds,time
           Datatype:   double
    plev     
           Size:       15x1
           Dimensions: plev
           Datatype:   double
           Attributes:
                       units         = 'Pa'
                       axis          = 'Z'
                       positive      = 'down'
                       long_name     = 'pressure'
                       standard_name = 'air_pressure'
    lat      
           Size:       96x1
           Dimensions: lat
           Datatype:   double
           Attributes:
                       bounds        = 'lat_bnds'
                       units         = 'degrees_north'
                       axis          = 'Y'
                       long_name     = 'latitude'
                       standard_name = 'latitude'
    lat_bnds 
           Size:       2x96
           Dimensions: bnds,lat
           Datatype:   double
    lon      
           Size:       192x1
           Dimensions: lon
           Datatype:   double
           Attributes:
                       bounds        = 'lon_bnds'
                       units         = 'degrees_east'
                       axis          = 'X'
                       long_name     = 'longitude'
                       standard_name = 'longitude'
    lon_bnds 
           Size:       2x192
           Dimensions: bnds,lon
           Datatype:   double
    hus      
           Size:       192x96x15x365
           Dimensions: lon,lat,plev,time
           Datatype:   single
           Attributes:
                       standard_name    = 'specific_humidity'
                       long_name        = 'Specific Humidity'
                       units            = '1'
                       cell_methods     = 'time: mean'
                       cell_measures    = 'area: areacella'
                       missing_value    = 1e+20
                       _FillValue       = 1e+20
                       associated_files = 'baseURL: http://cmip-

[Chad Greene]

What is your question?

Answer 1

[Walter Roberson]

Extract the stored pressure levels. Then use

mask = ismember(plev, [500, 700, 850, 1000]);

then

hus_subset = hus(:, :, mask, :);

Now you can create a new (or updated) nc file containing the subset.