Zack
0
I deal with lots of mathematical expressions in a certain Julia script and would like to know if storing such a formula as a String is ok, or whether using the Symbol data type is better. Thinking about scalability and keeping memory requirements to a minimum. Thanks!
Update: the application involves a machine learning model. Ideally, it should be applicable to big data too, hence the need for scalability.
In a string, each character is stored based on its number of codeunits, eg. 1 for ascii. The same is true for the characters of a Symbol. So that is a wash; do what fits your use best, probably Symbols since you are manipulating expressions.
An expression like :(x + y) is stored as a list of Any, with space allocated according to the sizeof each item in the expression.
In an expression like :(7 + 4 * 9) versus a string like "7 + 4 * 9" there are two conflicting issues. First, 7 is stored as 1 byte in the string, but 8 bytes in the expression since there are 64-bit Ints in play. On the other hand, whitespace takes up 1 byte each space in the string, but does not use memory in the expression. And a number like 123.123456789 takes up 14 bytes in the string and 8 in the expression (64 bit floats).
I think that, again, this is close to being even, and depends on the specific strings you are parsing. You could, as you work with the program, store both, compare memory usage of the resulting arrays, and drop one type of storage if you feel you should.