Scala row range

Question

In Ruby, we can do this:

$ irb >> ("aa".."bb").map { |x| x } => ["aa", "ab", "ac", "ad", "ae", "af", "ag", "ah", "ai", "aj", "ak", "al", "am", "an", "ao", "ap", "aq", "ar", "as", "at", "au", "av", "aw", "ax", "ay", "az", "ba", "bb"] 

In Scala, if I try the same to get the error:

 $ scala Welcome to Scala version 2.9.1 (OpenJDK 64-Bit Server VM, Java 1.7.0_51). scala> ("aa" to "bb").map(x => x) <console>:8: error: value to is not a member of java.lang.String ("aa" to "bb").map(x => x) ^ 

How to get row range in Scala?

Answer 1

In this example you can do (scala 2.10)

 val atoz = 'a' to 'z' for {c1 <- atoz if c1 <= 'b'; c2 <- atoz if (c1 == 'a' || (c1 == 'b' && c2 < 'c'))} yield s"$c1$c2" 

Edited according to the comment, thanks (but getting a little ugly!)

Answer 2

 ('a' to 'z').map("a" + _) :+ "ba" :+ "bb" 

:)

Answer 3

And for understanding it will be nice:

 val abc = 'a' to 'z' for (c1 <- abc; c2 <- abc) yield (s"$c1$c2") 

This gives Seq / Vector [String] with all the permutations you expect

Answer 4

Here is one possibility, assuming your characters should be in the range from 'a' to 'z'. The intToAlpha function intToAlpha not very pretty and is not symmetrical with alphaToInt , so you can find a better implementation.

 // "a" -> 0, "b" -> 1, "ba" -> 26, "bb" -> 27 etc. def alphaToInt(s: String) = (0 /: s) { (res, c) => res * 26 + c - 'a' } // reverse function to `alphaToInt` def intToAlpha(len: Int)(i: Int) = { val sb = new StringBuilder var j = i while (sb.length < len) { sb append ((j % 26) + 'a').toChar j /= 26 } sb.reverse.toString } def range(from: String, to: String) = alphaToInt(from) to alphaToInt(to) map intToAlpha(from.length) 

Test:

 range("aa", "bb") 

Alternative version:

 import annotation.tailrec @tailrec def intToAlpha(len: Int, res: String = "")(i: Int): String = if (len <= 0) res else { val c = ((i % 26) + 'a').toChar intToAlpha(len - 1, s"$c$res")(i / 26) } 

Answer 5

This is like a 26 * 26 matrix for each 2 char combination, we have a matrix (az * az):

 def scan(start:String, end:String) = { val row_start = start.toCharArray.head val column_start_of_first_row = start.toCharArray.last val row_end = end.toCharArray.head val column_end_of_last_row = end.toCharArray.last val printRow = (current_row:String, current_row_start_col:Char, current_row_end_col:Char) => (current_row_start_col to current_row_end_col).map( current_row + _ ) (row_start to row_end).map { current_row=> current_row match { case `row_start` => printRow(current_row.toString, column_start_of_first_row, 'z') case `row_end` => printRow(current_row.toString, 'a' , column_end_of_last_row) case _ => printRow(current_row.toString, 'a' , 'z') } }.reduce(_ ++: _) } println( scan("aa", "bb") ) println( scan("af", "bb") )