How to use a javascript function from an external script in lightning controller?

I want to load a function from external script and then use it in the component controller:

example of a function that i tried to call from the component controller (from the Init method specifically)

 function myFunction() {
    log.console('Hiiii'); 
} 

I loaded the script like that:

<ltng:require scripts="{!$Resource.DataArrays}"
    afterScriptsLoaded="{!c.doInit}" />

then i tried simply to call it from the Init method:

    doInit : function(cmp){

  myFunction();
}

It does not work, i got an error like this one:

Uncaught Action failed: c:realEstateFilterComponent$controller$doInit [myFunction is not defined]

Do you know to make it work ?