Saving data files in Julia

Shuvomoy Das Gupta

April 28, 2020

In this blog we will discuss ways of saving data into a file in Julia. We will discuss two methods of doing it: using JLD2 package and writing directly into a .jl file. The literate code for this blog is available at: this link.

Table of contents

Method 1: Using JLD2 Package

Probably the quickest method to save the relevant data is to use the package JLD2.

using JLD2

A = randn(5,5)

b = randn(5)

str = "hello world"

Suppose, we want to save the variables A, b, and str, so that we could load them later for some other purpose.

Saving is done by using the following command.

@save "example.jld2" A b str

Now suppose we want to load the variablesA, b, and str into our workspace. Then we can do that using the following command.

@load "example.jld2" A b str

Which will load the desired variables in our work space.

Method 2: Writing into a .jl File

Now, in some circles, people prefer to save their data into some sort of text file that can be opened and seen using notepad etc. In such case, we could proceed as follows.

output_file = open("output_file.jl","w") # this will create a file named output_file.jl, where we will write the data.

write(output_file, "# We are saving the variables A, b, and str \n \n") # this line will act as a comment in the original file

The following command will write A into output_file.jl

write(output_file, "A = ") # writes A =

show(output_file, A) # writes the content of A

write(output_file, "; \n \n") # puts a semicolon to suppress the output and two line breaks

The following command will write b into output_file.jl

write(output_file, "b = ") # writes b =

show(output_file, b) # writes the content of b

write(output_file, "; \n \n") # puts a semicolon to suppress the output and two line breaks

The following command will write str into output_file.jl

write(output_file, "str = ") # writes str =

show(output_file, str) # writes the content of str

write(output_file, "; \n \n") # puts a semicolon to suppress the output and two line breaks

Finally we close the file.

close(output_file)

The benefit of this method is that we can open output_file.jl as a normal julia file and observe the contents of A, b, str which are preferred by some people. If we open the file, it will look something similar to the following.

# We are saving the variables A, b, and c

A = [0.2660919202329622 0.3836364273856932 -0.0843680697224458 -0.41802388053627293 -0.3642969656325985; -1.6326433489594656 0.8264017202126758 0.822230872741246 -2.131477875645448 -0.47154398683850046; 0.44945692740036236 1.8601083201122803 0.21328754042393291 1.6337810748330106 0.22377743588354782; 0.4650833154598731 0.7577147546636607 -0.3759919034593861 -0.7268603483224291 -1.355544453370908; 1.22775636169604 -0.6810273422844582 0.39118388831225326 0.6436653188719305 0.7072677389318383];

b = [-0.4480408521367389, -0.2470478314562805, -0.5170341188440505, -0.5941415056081019, -1.3602127485958821];

str = "hello world";

To load the variables in this case, we just run the following command.

include("output_file.jl")

Some side note regarding generating the literate code: First, cd to the directory where the file is in by running the a command similar to the following. cd("C:\\Users\\shuvo\\Desktop") Then, run using Literate Finally, run Literate.markdown("name_of_the_file.jl", "."; documenter=false)

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