nccreate
Create variable in netCDF file
Description
nccreate(
creates a variable with additional options specified by one or more name-value arguments.
For example, to create a nonscalar variable, use the filename
,varname
,Name,Value
)Dimensions
name-value argument.
Examples
Create Variables in NetCDF File
Create a netCDF file named myexample.nc
that contains a variable
named Var1
.
nccreate("myexample.nc","Var1")
Create a second variable in the same file.
nccreate("myexample.nc","Var2")
Display the contents of the netCDF file.
ncdisp("myexample.nc")
Source: pwd\myexample.nc Format: netcdf4_classic Variables: Var1 Size: 1x1 Dimensions: Datatype: double Var2 Size: 1x1 Dimensions: Datatype: double
Specify Dimensions and File Format
Create a two-dimensional variable named peaks
in a netCDF-3
classic format file named myncclassic.nc
. Specify the name and length
of each dimension by using the Dimensions
name-value argument.
Specify the file format by using the Format
name-value
argument.
nccreate("myncclassic.nc","peaks", ... "Dimensions",{"r",300,"c",400},"Format","classic")
Write data to the variable.
ncwrite("myncclassic.nc","peaks",peaks(100))
Display the contents of the netCDF file.
ncdisp("myncclassic.nc")
Source: pwd\myncclassic.nc Format: classic Dimensions: r = 300 c = 400 Variables: peaks Size: 300x400 Dimensions: r,c Datatype: double
Input Arguments
filename
— Filename
string scalar | character vector
Filename, specified as a string scalar or character vector. Specify the name of an existing netCDF file or the name you want to assign to a new netCDF file.
Example: "myFile.nc"
varname
— Name of new variable
string scalar | character vector
Name of the new variable, specified as a string scalar or character vector.
If filename
specifies a file with format
netcdf4
, you can specify the location of the new variable within
the group hierarchy by specifying varname
as a fully qualified
name. In this case, nccreate
creates new groups as needed to place
the new variable at the specified location in the hierarchy.
Example: "myVar"
Example: "/myGrp/mySubGrp/myNestedVar"
Name-Value Arguments
Specify optional pairs of arguments as
Name1=Value1,...,NameN=ValueN
, where Name
is
the argument name and Value
is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.
Example: nccreate("myFile.nc","Var1",Datatype="double",Format="classic")
creates a variable named Var1
of type NC_DOUBLE
in a
netCDF-3 classic file named myFile.nc
.
Before R2021a, use commas to separate each name and value, and enclose
Name
in quotes.
Example: nccreate("myFile.nc","Var1","Datatype","double","Format","classic")
Dimensions
— Dimensions of variable
cell array
Dimensions of the new variable, specified as a cell array. The cell array lists
the dimension name as a string scalar or character vector followed by its numerical
length, in this form:
{dname1,dlength1,dname2,dlength2,...,dnameN,dlengthN}
. The
dname1
entry is the name of the first dimension, and
dlength1
is the length of the first dimension, specified as a
nonnegative integer or Inf
. Then dname2
is the
name of the second dimension, dlength2
the length of the second
dimension, and so on. A variable with a single dimension is treated as a column
vector.
For dimensions that already exist, specifying the length is optional. If you do specify the length of an existing dimension, it must match the current length.
Use a dimension length of Inf
or 0
to
specify an unlimited dimension. A file with format netcdf4
can have
any number of unlimited dimensions in any order; all other formats can have only one
unlimited dimension per file, and it must be specified last in the cell array.
nccreate
creates the dimension at the same location as the
variable. For files with format netcdf4
, you can specify a
different location for the dimension using a fully qualified dimension name.
Example: "Dimensions",{"dim1",100,"/mygroup/dim2",150,"dim3",Inf}
Data Types: cell
Datatype
— MATLAB® data type
"double"
(default) | "single"
| "int32"
| ...
MATLAB data type, specified as one of the values in this table. When
nccreate
creates the variable in the netCDF file, it uses the
corresponding netCDF data type.
Value of Datatype | NetCDF Variable Type |
---|---|
"double" | NC_DOUBLE |
"single" | NC_FLOAT |
"int32" | NC_INT |
"int16" | NC_SHORT |
"int8" | NC_BYTE |
"char" | NC_CHAR |
"uint64" (*) | NC_UINT64 |
"int64" (*) | NC_INT64 |
"uint32" (*) | NC_UINT |
"uint16" (*) | NC_USHORT |
"uint8" (*) | NC_UBYTE |
"string" (*) | NC_STRING |
(*) These values of Datatype
are available only for files
with format netcdf4
.
Example: "Datatype","int16"
Data Types: string
| char
Format
— NetCDF file format
"netcdf4_classic"
(default) | "netcdf4"
| "classic"
| "64bit"
NetCDF file format, specified as one of these values.
Value of Format | Description |
---|---|
"classic" | netCDF-3 |
"64bit" | netCDF-3, with 64-bit offsets |
"netcdf4_classic" | netCDF-4 classic model |
"netcdf4" | netCDF-4 (Use this format to enable group hierarchy) |
If varname
specifies a group (for example,
"/grid3/temperature"
), then nccreate
sets
the value of Format
to "netcdf4"
.
Example: "Format","64bit"
Data Types: string
| char
FillValue
— Replacement value for missing values
scalar | "disable"
Replacement value for missing values, specified as a scalar or
"disable"
. The default value is supplied by the netCDF library.
To disable replacement values, specify a value of "disable"
. You
cannot disable FillValue
when writing string data to files with
format netcdf4
.
Note
The nccreate
function assigns the value of
FillValue
to the _FillValue
attribute of
the new netCDF variable varname
. You cannot change the value of
this attribute after you have created the variable.
This argument is available only for files with format netcdf4
or netcdf4_classic
.
Example: "FillValue",0
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
| char
| string
ChunkSize
— Chunk size along each dimension
numeric vector
Chunk size along each dimension, specified as a numeric vector. The first element specifies the number of rows, the second element specifies the number of columns, the third element specifies the length of the third dimension, and so on. The default value is supplied by the netCDF library.
This argument is available only for files with format netcdf4
or netcdf4_classic
.
Example: "ChunkSize",[5 6 9]
Data Types: double
DeflateLevel
— Level of compression
0
(default) | integer scalar value between 0
and
9
Level of compression, specified as an integer scalar value between
0
and 9
. A value of 0
indicates no compression. A value of 1
indicates the least
compression, and a value of 9
indicates the most. You cannot set
DeflateLevel
if Datatype
is
"string"
.
This argument is available only for files with format netcdf4
or netcdf4_classic
.
Example: "DeflateLevel",5
Data Types: single
| double
| int8
| int16
| int32
| int64
| uint8
| uint16
| uint32
| uint64
Shuffle
— Status of shuffle filter
false
or 0
(default) | true
or 1
Status of the shuffle filter, specified as a numeric or logical
0
(false
) or 1
(true
). A value of false
disables the shuffle
filter, and true
enables it. The shuffle filter assists with the
compression of integer data by changing the byte order in the data stream. You cannot
enable the shuffle filter if Datatype
is
"string"
.
This argument is available only for files with format netcdf4
or netcdf4_classic
.
Example: "Shuffle",true
Data Types: logical
Tips
MATLAB interprets data as column major, but the netCDF C API interprets data as row major. Multidimensional data in the netCDF C API shows dimensions in the reverse of the order shown by MATLAB and consequently appears transposed.
Version History
Introduced in R2011aR2023b: Setting DeflateLevel
to 0
disables the deflate filter
Setting the compression level to zero disables the deflate filter. Previously, the deflate filter could be enabled with a compression level of zero.
R2023b: Use compression and shuffle filter only with fixed-length data types
Compression and the shuffle filter can be used only with fixed-length data types and
generate an error if applied to variables of type NC_STRING
. Previously,
if you specified compression or the shuffle filter for NC_STRING
variables, the specification had no effect.
R2021b: Define NC_STRING
data
You can define NC_STRING
data in netCDF-4 files.
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