After having opened the file, use the "Write File" function to write the 2D array that you wire on "data" input. Also wire the "header" input to "True". To read data back from file, use "Read File" function wiring a 2D array (may be empty, just the datatype is needed) to the "byte stream type" input. File data comes from the "data" output.
The header input of "Write File" function works like this:
False: variable length data (arrays and strings) are written as individual elements, that means that writing a MxN array writes M*N elements on file, without dimension or length information. Only the content of strings is written.
True: the data is preceded by a header that tells the number of dimension(s) in the array and the size of each dimension. That all
ows to recover on read the binary array along with its size. Strings are preceded with the length on the string so when you call the "Read File" function with a string wired to "byte stream type", a string of the length stored in the header is read.