Trouble reading/writing .mat files

[lawsofthought]

Trying to write a .mat file, I get an error.

library('rio')

Df <- data.frame(x = rnorm(10),
                 y = rnorm(10),
                 z = rnorm(10))


export(Df, "foo.mat")

Error in .export.default(file = file, x = x, ...) : Format not supported

So, I try

export(Df, "foo.mat", format='matlab')

and that works without complaint, and I can load foo.mat in octave and it looks good (but it is three 10 element vectors, x, y, and z).

Now, I try to read it in.

X <- import("foo.mat")

and trouble

Error in .import.default(file = file, ...) : Format not supported

So, I try,

X <- import("foo.mat", format='matlab')

but, although no errors, I get

> X
[1] x y z
<0 rows> (or 0-length row.names)

For comparison,

library(rmatio)
X <- read.mat('foo.mat')

and that works fine

> X
$x
 [1] -1.0852233  1.0429430  0.5547360  0.3567666  0.1246707  1.0751442  1.0522228 -0.8839636  0.5240233  0.7145037

$y
 [1]  1.2250672 -0.2555996  0.8573036 -2.6395863 -0.6556084  2.0775326  1.7713386 -1.3604206  0.5656115 -1.1923609

$z
 [1] -0.5950004  0.4543115 -0.9667500  2.5074521 -0.8083928 -0.1983492  0.4709925  0.1480296  0.6565982 -0.5104466

Am I missing a trick?

> sessionInfo()
R version 3.4.3 (2017-11-30)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Arch Linux

Matrix products: default
BLAS: /usr/lib/libblas.so.3.8.0
LAPACK: /usr/lib/liblapack.so.3.8.0

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C               LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8    
 [5] LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8    LC_PAPER=en_GB.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       

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

other attached packages:
[1] rmatio_0.12.0 rio_0.5.5    

loaded via a namespace (and not attached):
 [1] Rcpp_0.12.11        lattice_0.20-35     grid_3.4.3          cellranger_1.1.0    magrittr_1.5        pillar_1.0.1       
 [7] rlang_0.1.6         readxl_1.0.0        curl_3.1            data.table_1.10.4-3 Matrix_1.2-12       openxlsx_4.0.17    
[13] forcats_0.2.0       tools_3.4.3         foreign_0.8-69      yaml_2.1.16         compiler_3.4.3      haven_1.1.0        
[19] tibble_1.4.1