Scala: Convert a string to string array with and without split given that all special characters except "(" an ")" are allowed

Question

I have an array

val a = "((x1,x2),(y1,y2),(z1,z2))"

I want to parse this into a scala array

val arr = Array(("x1","x2"),("y1","y2"),("z1","z2"))

Is there a way of directly doing this with an expr() equivalent ? If not how would one do this using split

Note : x1 x2 x3 etc are strings and can contain special characters so key would be to use () delimiters to parse data -

Code I munged from Dici and Bogdan Vakulenko

val x2 = a.getString(1).trim.split("[\()]").grouped(2).map(x=>x(0).trim).toArray

val x3 = x2.drop(1) // first grouping is always null dont know why

var jmap = new java.util.HashMap[String, String]()

for (i<-x3)
{
 val index = i.lastIndexOf(",")
 val fv = i.slice(0,index)
 val lv = i.substring(index+1).trim
 jmap.put(fv,lv)
}

This is still suceptible to "," in the second string -

Is the second snippet an array of strings, or is x1 (for example) a variable? Also, I think not using split is an unncessary constraint. Why don't you want to use it? — Dici
– Dici, Commented Dec 14, 2018 at 13:25
Spark has this useful feature for expr() which directly evaluates the expression - This is already in the format that we declare arrays in scala so splitting is needless if it can be avoided - Also I am assuming split will be long code - — Leothorn
– Leothorn, Commented Dec 14, 2018 at 13:30
I didn't downvote. If you're using this with Spark, please say it in the question. Also, I still don't get your second snippet. Is x1 a variable or is it the string "x1" ? — Dici
– Dici, Commented Dec 14, 2018 at 13:31
I didnt add spark because this is not a dataset / frame purely a string not a part of any dataframe - And yes its a string not variable — Leothorn
– Leothorn, Commented Dec 14, 2018 at 13:33
But expr in Spark is a very different thing, it's just syntactic sugar for generating a SQL-like query. Here we're talking about pure Scala, expr will be useless. You have to parse this string, and the most sensible way to do it is to use split. — Dici
– Dici, Commented Dec 14, 2018 at 13:35

Dici · Accepted Answer · 2018-12-14 13:48:52Z

2

Actually, I think regex are the most convenient way to solve this.

val a = "((x1,x2),(y1,y2),(z1,z2))"
val regex = "(\\((\\w+),(\\w+)\\))".r
println(
  regex.findAllMatchIn(a)
       .map(matcher => (matcher.group(2), matcher.group(3)))
       .toList
)

Note that I made some assumptions about the format:

no whitespaces in the string (the regex could easily be updated to fix this if needed)
always tuples of two elements, never more
empty string not valid as a tuple element
only alphanumeric characters allowed (this also would be easy to fix)

edited Dec 14, 2018 at 13:48

answered Dec 14, 2018 at 13:46

Dici

26k7 gold badges45 silver badges86 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Leothorn Over a year ago

Damn i need to master regex :/ its like a disability without it

Dici Over a year ago

It can be useful sometimes, just don't over-use it :D If you want Hackerrank has some regex problems to train you on. Also use tools such as this one while training: regex101.com

Leothorn Over a year ago

I found that x1 and x2 may have special characters in them . How would we edit this code to hande that

Dici Over a year ago

What kind of special characters? What would be the input and desired output?

Leothorn Over a year ago

- hyphens - , commas & ampersands - We cant get rid of them - I munged your code to get this - i dont know if it helps - i added some code in the question itself

|

Bogdan Vakulenko · Accepted Answer · 2018-12-14 17:27:21Z

1

val a = "((x1,x2),(y1,y2),(z1,z2))"

a.replaceAll("[\\(\\) ]","")
 .split(",")
 .sliding(2)
 .map(x=>(x(0),x(1)))
 .toArray

edited Dec 14, 2018 at 17:27

answered Dec 14, 2018 at 13:44

Bogdan Vakulenko

3,3901 gold badge12 silver badges29 bronze badges

5 Comments

Leothorn Over a year ago

Thanks this is elegant as well

Leothorn Over a year ago

How does one handle spaces and special characters for this is x1 ,x2,y1,y2 are strings with spaces and - ?

Bogdan Vakulenko Over a year ago

just add characters that you want to ignore to replaceAll. I've edited the answer and added space in there.

Bogdan Vakulenko Over a year ago

"[\\(\\) ]" - this is the place where to add characters to be replaced with empty string.

Dici Over a year ago

Note: you don't need to escape parentheses inside of the square brackets (whatever is inside of them is interpreted as a simple character)

Collectives™ on Stack Overflow

Scala: Convert a string to string array with and without split given that all special characters except "(" an ")" are allowed

2 Answers 2

7 Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

7 Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related