Simple Character Indexing Comments

General:This frame introduces you to simple indexing principals in Glee. These examples correspond to the examples given for numeric vectors. This demonstrates another characteristic of Glee ... learn a concept and it holds for all types.

Simple Indexing: From the character string 'abcdef' the elements (7 6 5 4 3 2 1 0) are extracted in that order yielding ( fedcba ). I use the :hex method for strings to show the result in hexadecimal form. For strings, invalid indexes yield spaces. This is inconsistent with what we did with numbers. With numbers we assumed the value at the index and nil outside the range of valid indices. This had some rationale for numerics but for characters, space makes mores sense.

Insert Indexing: When you index with a fractional index, this tells Glee you want to insert elements into the result. The integer indices you already understand from the previous example. But decimal indices tell Glee to open a space for the value. In this example, 1.1 leaves a space in the result. Notice there is nothing at vector position 0 so those indexes also yield space. I also illustrate saving a value into a variable ('abcd'=>a;) as I did with the numeric examples. I can then reference the variable (in this case "a") in the indexing operation as (a[0 0.1 1 1.1 2 2.1 3 3.1 4 4.1]) yielding (  a b c d ). Again, the :hex method makes the spaces easier to see.

Indexing with index generators: We begin with the string ('abcdefghi'=>a;). (a[2..5] $;) indexes the 2nd through 5th element using range. (a[4` +1] $;) does the same using a calculated index. They both yield the same (bcde).

Indexed Assignment: You can use Indexed assignment to change the contents of variables. This example shows three statements.
Statement 1: ('abcde'=>a;) creates a variable a.
Statement 2:('CD'=>[3 4]a;) assigns the elements of the string 'CD'into the 3rd and 4th element of a.
Statement 3: (a:hex $; ) then displays the resulting "a" after the changes yielding (abCDe).

Indexed Assignment: Here with ('DCX'=>[4 3 9 2]a;) we have the case of more indexes than data. Again, as with numbers, Glee does the left take on the left argument to even things out. But where numbers drag the last numeric value from the right, this isn't really appropriate for strings. So strings drag spaces from the right giving "D" "C" "X" "space". The "X" tries to go into element 9 (which is nowhere). The the 4th element of the left argument (now a space) is indexed into the 2nd position of "a".

Showing Explicit Left Take: This example produces the same result as the previous one. Only this time we do the left take explicity ('DCX'<-4 $ ) and display the intermediate result with the $ ("DCX ").

Boolean indexing (or selection):In the numeric example, we created the boolean indexes using a logical operation (e.g. >). Here I illustrate using Glee's special boolean notation in a character string. If the string contains only 1's and 0's and is used as an index, Glee interprets it as a boolean vector. So ('abcdef'["11001101"]) yields (abef .) selecting at every 1 and rejecting at every 0. Remaining consistent, indexing into an invalid position yields spaces.

Empty Index: As with all Glee objects, an empty index causes a copy of the object's contents to be returned, in this case ( abcdef  )