I'm trying to create an hdf5 file using R's rhdf5 package.

I want to create this group hierarchy: "top/bottom". In "bottom", I'd like to have two datasets (both H5S_SCALARs):

1. "score" which is an "H5T_IEEE_F64LE" type
2. "type" which is an "H5T_STRING" type

I thought this would work:

output.path <- "my.h5.dir"
dir.create(output.path,recursive = T)
h5.file <- rhdf5::H5Fcreate(paste0(output.path,"/test.h5"))

top.group <- rhdf5::H5Gcreate(h5.file,"top")
bottom.group <- rhdf5::H5Gcreate(top.group,"_bottom")

h5.space <- rhdf5::H5Screate(type="H5S_SCALAR")
h5.dataset <- rhdf5::H5Dcreate(h5loc=bottom.group,name="score",dtype_id="H5T_IEEE_F64LE",h5space=h5.space)
rhdf5::H5Dwrite(h5.dataset,array(c(1,2)))
rhdf5::H5Dclose(h5.dataset)
rhdf5::H5Sclose(h5.space)

h5.space <- rhdf5::H5Screate(type="H5S_SCALAR")
h5.dataset <- rhdf5::H5Dcreate(h5loc=bottom.group,name="type",dtype_id="H5T_STRING",h5space=h5.space)
rhdf5::H5Dwrite(h5.dataset,"text")
rhdf5::H5Dclose(h5.dataset)
rhdf5::H5Sclose(h5.space)

However,

h5.dataset <- rhdf5::H5Dcreate(h5loc=bottom.group,name="type",dtype_id="H5T_STRING",h5space=h5.space)

throws this error:

Error in rhdf5::H5Dcreate(h5loc = bottom.group, name = "type", dtype_id = "H5T_STRING",  : 
  HDF5. Invalid arguments to routine. Inappropriate type.

Although I do see the H5T_STRING type:

> "H5T_STRING" %in% rhdf5::h5const("H5T")
[1] TRUE

Any idea?

BTW this also happens if I try:

h5.space <- rhdf5::H5Screate(type="H5S_SIMPLE")

h5.dataset <- rhdf5::H5Dcreate(h5loc=bottom.group,name="val",dtype_id="H5T_STD_I64LE",h5space=h5.space)


Error in rhdf5::H5Dcreate(h5loc = bottom.group, name = "val", dtype_id = "H5T_STD_I64LE",  : 
  HDF5. Dataset. Unable to initialize object.

> sessionInfo()
R version 3.3.3 (2017-03-06)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X El Capitan 10.11.6

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] rhdf5_2.16.0

loaded via a namespace (and not attached):
[1] zlibbioc_1.18.0 tools_3.3.3    

So this example demonstrates how to write a single column dataset containing strings of up to length 10 characters (you can set the limit).

I haven't tried any of your other examples yet, but thank you for listing them. I'll create a Github issue to remind me to look at them later.

I'm not sure the H5T_STRING should be listed in the output from rhdf5::h5const("H5T"), I think this may be an error in the rhdf5 code so I'll check that too.

library(rhdf5)

## file to create
file_name <- '/tmp/test.h5'

## character strings we're going to add to the file
text <- c("text", "text2", 'abcdefghijklmnop')

## create file and 
h5.file <- H5Fcreate(file_name)
top.group <- H5Gcreate(h5.file,"top")

## our string dataset is one-dimensional and
## as long as the number of strings we want to add
h5.space <- H5Screate_simple(dims = length(text), 
                             maxdims = length(text))

## create a string datatype
## this example allows strings upto length 10
## it will truncate any longer like our 3rd entry above
tid <- H5Tcopy(dtype_id="H5T_C_S1")
H5Tset_size(tid, size = 10L)

## if you don't want truncated, so something like
## H5Tset_size(tid, size = max(nchar(text))+1)

## cratee and write the dataset
h5.dataset <- rhdf5::H5Dcreate(h5loc = top.group,
                               name = "type",
                               dtype_id = tid,
                               h5space = h5.space)
rhdf5::H5Dwrite(h5.dataset, buf = text)

## close everything
H5Dclose(h5.dataset)
H5Sclose(h5.space)
H5Gclose(top.group)
H5Fclose(h5.file)