Contents
Substring Replacement
x replace p;q replaces all occurrences of p by q in x .
replace=: 4 : 0
'p q'=. y
j=. p nosindx x
if. ''-:j do. x return. end.
d=. p-&#q
k=. (j+(0>.-d)*i.#j)+/i.#q
select. *d
case. 1 do. (0 (j+/(#q)+i.d)}1$~#x) # q k}x
case. 0 do. q k}x
case. _1 do. q k} (0 (d{."1 k)}1$~(#x)+(#j)*|d) #^:_1 x
end.
)
nosindx=: 4 : 0
s=. x I.@E. y
i=. s I. s+#x
(i.&_1 {. ]) (s,_1) {~ (i,_1) {~^:a: 0
)replace uses nosindex , adapted from Non-Overlapping Substrings to find the indices of non-overlapping substring occurrences. nosindex is equivalent to I.@E. if substring occurrences do not overlap (i.e. if no non-trivial prefix of p is a suffix of p ).
Examples of replace in use:
x=: 'of the people, by the people, for the people' x replace 'the';'a' of a people, by a people, for a people x replace 'the';'one' of one people, by one people, for one people x replace 'the';'them there' of them there people, by them there people, for them there people
Program Logic
Let d=. p-&#q be the difference between the length of p (the target string) and the length of q (the replacement string). The processing depends on whether d is positive, zero, or negative:
If d is positive ( p longer than q ), some characters will be removed from x after it is amended by q .
If d is zero ( p has the same length as q ), x is simply amended by by q .
If d is negative ( p is shorter than q ), x is first expanded to make room and then amended by q .
If j=. x nosindex p are the indices of non-overlapping occurrences of p in x , then k=. (j+(0>.-d)*i.#j)+/i.#q are the indices to be amended. If d is not negative, i.e. if p is not shorter than q , k simplifies to j+/i.#q ; if d is negative ( p is shorter than q ), the indices of p in the expanded string are j+(-d)*i.#j .
The following examples illustrate the three cases:
x=: 'of the people, by the people, for the people' p=: 'the' ] j=: p nosindx x 3 18 34
p is longer than q (d>0)
q=: 'a'
] d=: p-&#q
2
j
3 18 34
j+(0>.-d)*i.#j
3 18 34
] k=. (j+(0>.-d)*i.#j)+/i.#q
3
18
34
q k} x
of ahe people, by ahe people, for ahe people
'.1' {~ b=. 0 (j+/(#q)+i.d)}1$~#x
1111..1111111111111..11111111111111..1111111
b # q k} x
of a people, by a people, for a people
p has the same length as q (d=0)
q=: 'one' ] d=: p-&#q 0 j 3 18 34 j+(0>.-d)*i.#j 3 18 34 ] k=. (j+(0>.-d)*i.#j)+/i.#q 3 4 5 18 19 20 34 35 36 q k} x of one people, by one people, for one people
p is shorter than q (d<0)
q=: 'them there'
] d=: p-&#q
_7
j
3 18 34
j+(0>.-d)*i.#j
3 25 48
] k=. (j+(0>.-d)*i.#j)+/i.#q
3 4 5 6 7 8 9 10 11 12
25 26 27 28 29 30 31 32 33 34
48 49 50 51 52 53 54 55 56 57
d{."1 k
6 7 8 9 10 11 12
28 29 30 31 32 33 34
51 52 53 54 55 56 57
'.1' {~ b=: 0 (d{."1 k)}1$~(#x)+(#j)*|d
111111.......111111111111111.......1111111111111111.......1111111
b #^:_1 x
of the people, by the people, for the people
q k} b#^:_1 x
of them there people, by them there people, for them there people
Non-Overlapping Occurrences
As stated above, nosindx finds the indices of non-overlapping substring occurrences. It is the same as I.@E. if substring occurrences do not overlap. What if they do overlap?
] x=: 40$'abcabcabc_' abcabcabc_abcabcabc_abcabcabc_abcabcabc_ x replace 'abcabc';'syzygy' syzygyabc_syzygyabc_syzygyabc_syzygyabc_ ] j0=: 'abcabc' I.@E. x 0 3 10 13 20 23 30 33 ] j1=: 'abcabc' nosindx x 0 10 20 30 x abcabcabc_abcabcabc_abcabcabc_abcabcabc_ '1' j0} '.'$~#x 1..1......1..1......1..1......1..1...... '1' j1} '.'$~#x 1.........1.........1.........1......... 'syzygy' (j0+/i.6)} x syzsyzygy_syzsyzygy_syzsyzygy_syzsyzygy_ 'syzygy' (j1+/i.6)} x syzygyabc_syzygyabc_syzygyabc_syzygyabc_ x replace 'abcabc';'syzygy' syzygyabc_syzygyabc_syzygyabc_syzygyabc_
Contributed by RogerHui.