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How to read netcdf files containing string arrays?

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I have a netCDF file which consists of a float array and a string array as verified by ncdump. In Matlab, I am able to load the float array, but I fail in loading the string array.
In particular, ncread produces an error:
ncread('string_test.nc','StringArray')
Error using netcdf.getVar (line 130)
12 is not a recognized netCDF datatype.
"12" is the code for NC_STRING and it seems like Matlab can not handle that.
The .nc file I'm trying to load can be downloaded from http://piotr.majdak.com/temp/netcdf/ where also more description is available.
I'm using Matlab 2011b - any ideas what I can do?

Accepted Answer

per isakson
per isakson on 5 Mar 2013
Edited: per isakson on 5 Mar 2013
I use R2012a.
ncdisp says: Datatype: UNSUPPORTED DATATYPE. See below. Why not accept that? What is the source of string_test.nc?
HDFView 2.9 reads string_test.nc as if it was an HDF5-file. So does Matlab's h5disp and h5read.
>> ncdisp( 'string_test.nc')
Source:
h:\m\cssm\string_test.nc
Format:
netcdf4
Dimensions:
test = 4
Variables:
FloatArray
Size: 4x1
Dimensions: test
Datatype: single
StringArray
Size: 4x1
Dimensions: test
Datatype: UNSUPPORTED DATATYPE
>> str = h5read( 'h:\m\cssm\string_test.nc', '/StringArray' )
str =
'NH10'
'CI03'
'HI17'
'NH11'
>>
>> h5disp( 'h:\m\cssm\string_test.nc', '/StringArray' )
HDF5 string_test.nc
Dataset 'StringArray'
Size: 4
MaxSize: 4
Datatype: H5T_STRING
String Length: variable
Padding: H5T_STR_NULLTERM
Character Set: H5T_CSET_ASCII
Character Type: H5T_C_S1
ChunkSize: []
Filters: none
Attributes:
'DIMENSION_LIST': H5T_VLEN
  3 Comments
Piotr Majdak
Piotr Majdak on 6 Mar 2013
I'm slowly coming to a similar conclusion. Thanks for the help.

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More Answers (3)

Peter Kuma
Peter Kuma on 20 Aug 2018
Just to let others know, I have submitted a new bug report (since I could not find the one submitted by Erik). The answer was:
As you correctly pointed out, this is a current limitation of the
netCDF implementation. It is being actively investigated for
enhacement.
The workaround is to utilize the fact that netCDF4 formats are a
subset of the HDF5 format and we can utilize the HDF5 functionality
to read the data
Workaround:
Instead of ncdisp, ncread utilize h5disp, h5read
I hope the above workaround solves your issue. If you have any
further queries, please reach out to me.
  1 Comment
Anna Weeks
Anna Weeks on 21 Aug 2018
The ability to write a mapped array section of values into a netCDF variable (i.e the 'NF_PUT_VARM_ type' functionality) would be highly desirable.

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Maxime Hervo
Maxime Hervo on 31 Mar 2017
Is there any update for this issue ? I still have the same problem with MATLAB R2016b !

liu jibao
liu jibao on 31 Jan 2018
Is there any update for this issue ? I still have the same problem with MATLAB R2017b !
  2 Comments
Natalie Perlin
Natalie Perlin on 24 Jul 2019
Thank you for filing the report, I wonder if anything has been done since then!
I have the same problem with Matlab not being able to read string variables in R2017a, R2018b.

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