str_rel

str_rel{s:str, sep:str, r{seq:int, ss:str}}

A relation generator. Can convert string s into substrings (ss) and vice-versa.

If sep is provided it is used to split the string (or join the substrings) otherwise no separator is used and the string is split (or joined) by character.

If sep is "\N", where N is an integer, the splits are in groups of N characters.

If sep is "\b", the splits/joins are byte-based.

{seq:int} is used to sequence the substrings.

Examples

split into characters

str_rel(s:="hello world")

sep
r

seq
ss
0
h
1
e
2
l
3
l
4
o
5
 
6
w
7
o
8
r
9
l
10
d

str_rel has taken the str s and converted it into a nested relation, r (hence the name: str_rel)

find the position(s) of the space characters

str_rel(s:="this has spaces")..r[ss=" "]

seq
ss

4
 
8
 

join words

str_rel(r:={seq:int,ss:str}{[0,"hello"],[1,"world"],}, sep:=" ")

s

hello world

bulk apply via composition to get reversed CITY

$S{*, s:=CITY}(str_rel){*, r:=r{*, seq:=-seq}}(str_rel){*, YTIC:=s}

SNO
SNAME
STATUS
YTIC

S1
Smith
20
nodnoL
S2
Jones
10
siraP
S3
Blake
30
siraP
S4
Clark
20
nodnoL
S5
Adams
30
snehtA

Note: since the second str_rel builds left to right, from smallest seq to largest, we can reverse the strings by inverting the seq provided by the first str_rel using seq:=-seq.

To see how this works here's the intermediate relation, after the first composition:

$S{*, s:=CITY}(str_rel)

SNO
SNAME
STATUS
sep
r

S1
Smith
20
seq
ss
0
L
1
o
2
n
3
d
4
o
5
n
S2
Jones
10
seq
ss
0
P
1
a
2
r
3
i
4
s
S3
Blake
30
seq
ss
0
P
1
a
2
r
3
i
4
s
S4
Clark
20
seq
ss
0
L
1
o
2
n
3
d
4
o
5
n
S5
Adams
30
seq
ss
0
A
1
t
2
h
3
e
4
n
5
s