Error "Could not open file 'ncfiles'". when using a for loop to open ncfiles

Hi

I have 469 ncfiles and I open them in a loop:

ncfiles = dir('*.nc') ;
Nfiles = length(ncfiles) ;     
for i = 1:Nfiles;
    ncdisp(ncfiles(i).name) ;  
    ncid=netcdf.open('ncfiles','NOWRITE');
    varname = netcdf.inqVar(ncid);
    [ndim, nvar, natt, unlim]=netcdf.inq(ncid);
end

But when I run the code I got the error when I used ncid:

Error using netcdf.open (line 52)

Could not open file 'ncfiles'.

Error in Blocking (line 9)

ncid=netcdf.open('ncfiles','NOWRITE');

I hope you can help me!

Answer 1

[Walter Roberson]

your file name is stored in ncfiles(i).name rather than being the literal file name 'ncfiles'

[Jonas Damsbo]

Hmm, I still got the error:

Error using netcdf.open (line 52)

Could not open file 'ncfiles(i).name'.

Error in Blocking (line 11)

ncid=netcdf.open('ncfiles(i).name','NOWRITE');

[Walter Roberson]

not 'ncfiles(i).name' just ncfiles(i).name without the '

[Jonas Damsbo]

I just try it before you have writing and it's works - thank!

[Jonas Damsbo]

Hi

Maybe you can tell me how I can define my variables from my nc files?

ncfiles = dir('*.nc') ;
Nfiles = length(ncfiles) ;     
for i = 1:Nfiles;
    ncdisp(ncfiles(i).name) ;  
    ncid=netcdf.open(ncfiles(i).name,'NOWRITE');
    [ndim, nvar, natt, unlim]=netcdf.inq(ncid);
end

%Defines longitudes, latitudes, time and z
lon = ncread(ncfiles(i).name,'longitude') ; nx = length(lon) ;
lat = ncread(ncfiles(i).name,'latitude') ; ny = length(lat) ;
time = ncread(ncfiles(i).name,'time') ; nt = length(time);
z = ncread(ncfiles(i).name,'z') ; nz = length(z);

Right now I get my different variables:

lat = 181 x 1 (181 values of size 9.9692e + 36)

lon = 360 x 1 (181 values of size 9.9692e + 36)

time = []

z = []

[Walter Roberson]

Every iteration you are overwriting ndim and so on . You are also not closing ncid .

The information about variables including their names can be extracted using ncinfo() instead of going into netcdf.* .

You can use dynamic field names to store variables:

loaded_file{i}.(these_variable_names{K})) = ncread(FILENAME, these_variable_names{K});

If you can count on the files all having the same variable names then use (i) instead of {i}

[Jonas Damsbo]

Okay so I try this:

ncfiles = dir('*.nc') ;
Nfiles = length(ncfiles) ;     
for i = 1:Nfiles;
    ncdisp(ncfiles(i).name) ; 
    ncid=netcdf.open(ncfiles(i).name,'NOWRITE');
    %[ndim, nvar, natt, unlim]=netcdf.inq(ncid);
    netcdf.close(ncid);
end

ncvars = {'longitude','latitude','time','z'};

for i = 1:Nfiles
  lon(i) = ncread(ncfiles(i).name, ncvars{1}); nx = length(lon(i));
  lat(i) = ncread(ncfiles(i).name, ncvars{2}); ny = length(lat(i));
  time(i) = ncread(ncfiles(i).name, ncvars{3}); nt = length(time(i));
  z(i) = ncread(ncfiles(i).name, ncvars{4}); nz = length(z(i));                                                                                                                                      
end

But now I get the error "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side".

My files have the same variables. The left side and the right side - it is thes sizes in ncread?

[Walter Roberson]

The result of ncread() is the complete content of the variable you indicate to read. That will not generally be a scalar, but you are assigning it to a scalar location.

You should consider using cell arrays. And watch out because length() is the max() of the dimensions, not any one particular dimension.

[Jonas Damsbo]

Such like that?

%Indlæser alle filer fra folderen
ncfiles = dir('*.nc') ;
Nfiles = length(ncfiles) ;     
for i = 1:Nfiles;
    ncdisp(ncfiles(i).name) ;  
    ncid=netcdf.open(ncfiles(i).name,'NOWRITE');
    %[ndim, nvar, natt, unlim]=netcdf.inq(ncid);
    netcdf.close(ncid);
end

lat = cell(Nfiles, 1);
lon = cell(Nfiles, 1);
time = cell(Nfiles, 1);
z = cell(Nfiles, 1);

for i = 1:Nfiles
  lon(i) = ncread(ncfiles(i).name, 'longitude'); %nx = length(lon(i));
  lat(i) = ncread(ncfiles(i).name, 'latitude'); %ny = length(lat(i));
  time(i) = ncread(ncfiles(i).name, 'time'); %nt = length(time(i));
  z(i) = ncread(ncfiles(i).name, 'z'); %nz = length(z(i));                                                                                                                                      
end

Because now I get the error "Conversion to cell from single is not possible."

[Walter Roberson]

lon{i} = ...