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Question

如何在julia的NetCDF文件中添加字符数组？下面是一个代码示例。首先，它已经给出了写一个字符串数组的错误，所以可能有些错误。但实际上，我需要“国家”为Char类型。如何将字符串数组更改为Char以在NetCDF中使用？这似乎与此问题（https://github.com/JuliaLang/julia/issues/17694）有关，但我看不出如何解决它。

示例：

using NetCDF
filename="test_netcdf_string.nc"
# Define some attributes
varatts = Dict("longname" => "number of citizens","units" => "million")
timeatts = Dict("longname" => "Time","units"    => "year")
nameatts = Dict("longname" => "Country name")

#Add some random data
time_data=collect(2014:2017)
countries=["Italy ","Germany", "France "]
cit_numbers=rand(5:100,size(countries,1),size(time_data,1))

#Create variable in netcdf
nccreate(filename, "citizens", "country", countries, nameatts,
"time", time_data, timeatts, atts=varatts)

ERROR: MethodError: no method matching nc_put_vara_x(::NetCDF.NcVar{Float64,1,6}, ::Array{UInt64,1}, ::Array{UInt64,1}, ::Array{String,1})

Answer 1

我不知道如何使用包NetCDF.jl执行此操作，但是这是使用julia包NCDatasets.jl执行此操作的方法。

using NCDatasets

filename="test_netcdf_string.nc"

time_data=collect(2014:2017)
countries=["Italy ","Germany", "France "]
cit_numbers=rand(5:100,size(countries,1),size(time_data,1))

ds = Dataset(filename,"c")
# define the dimensions
defDim(ds,"countries",length(countries))
defDim(ds,"time",length(time_data))

# define the variables
nccit_numbers = defVar(ds,"cit_numbers",Float64,("countries","time"))
nccountries = defVar(ds,"countries",String,("countries",))
nctime = defVar(ds,"time",Float64,("time",))

# define the attributes
nccountries.attrib["longname"] = "Country name"
# add more attributes...

nccountries[:] = countries
nccit_numbers[:] = cit_numbers
nctime[:] = time_data

# closing the file to make sure the data is saved
close(ds)

运行julia命令Dataset(filename)会返回：

Dataset: test_netcdf_string.nc
Group: /

Dimensions
   countries = 3
   time = 4

Variables
  cit_numbers   (3 × 4)
    Datatype:    Float64
    Dimensions:  countries × time

  countries   (3)
    Datatype:    String
    Dimensions:  countries
    Attributes:
     longname             = Country name

  time   (4)
    Datatype:    Float64
    Dimensions:  time

如果有人可以为包NetCDF.jl添加答案，这会有所帮助。

请注意，从版本4开始，将字符串列表（或数组）写入NetCDF文件已添加到NetCDF库中。您将找到大量有关NetCDF库3的文档，您只能编写一个向量（或数组） ）单个字符。在这种情况下，您需要使所有国家/地区名称长度相等（例如，用空格填充它们或使用空字符填充它们）并将所有这些名称组合成一个矩阵。幸运的是，NetCDF 4不再需要这样做了。