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The aim is to trim elements in from the ends of a list, depending on if they are in a second list of "falsey" results.
For example, if the first list is [-1, 1, 2, 0, -1, 3, -1, 4, -1, -1] and the second is [-1], then we would remove all leading and trailing -1s from the first input, but not any -1s in the middle: [1, 2, 0, -1, 3, -1, 4]
You may take input in any allowed method and this is code-golf so the shortest code in bytes wins.
f v|g<-reverse.snd.span(`elem`v)=g.g
f v -- define a function f that takes as input a list v of falsey values
|g<- -- inside the definition, define a new function g that...
reverse -- reverses...
.snd -- the second element of...
.span -- a tuple (say (x,y)) where x is the longest prefix of elements that...
(`elem`v) -- belong to v...
-- and y is the rest of the list
=g.g -- f is defined as the composition g.g (basically apply g twice)
snd.span for dropWhile
\$\endgroup\$
F and take the two inputs separately?
\$\endgroup\$
Mar 30, 2021 at 21:30
math.unicode, 19 bytes[ '[ _ ∈ ] trim ]
It's a quotation (anonymous function) that takes two sequences as input and returns one sequence as output.
'[ _ ∈ ] Push a fried quotation to the data stack to be used later by trim. Whatever is on top of the data stack gets slotted into the quotation at the _. This will be the list of elements to trim.trim Take a sequence and a quotation and apply the quotation to elements on both ends of the sequence, removing elements for which the quotation returns t. Stop when f is encountered.∈ Take an object and a sequence and return t if the object is in the sequence. Shorthand for member?.Anonymous infix function.
⌂deb
A library function: delete ending blanks using the left argument as a list of what is considered "blanks".
a->b->a.dropWhile(b::contains).sorted((c,d)->-1).dropWhile(b::contains).sorted((c,d)->-1)
a->b->{int i=-1,j=a.length;for(;b.contains(a[++i]););for(;b.contains(a[--j]););return java.util.Arrays.copyOfRange(a,i,j+1);}
-16 bytes thanks to @Original Original Original VI
(a,s,g=x=>s.includes(x[0])?g(x.slice(1)):x.reverse())=>g(g(a))
Old:
a=>n=>(t=z=>z.findIndex(d=>!n.includes(d)),a.slice(t(a),-t([...a].reverse())))
Can probably be shortened by a ton
f([-1, 1, 2, 0, -1, 3, -1, 4, -1, -1])([2, -1, 1]) seems to give an empty array, am I doing something wrong or is there a bug in the code?
\$\endgroup\$
Mar 30, 2021 at 18:33
s=>1.to(2)./:(_)((a,_)=>a.reverse dropWhile s)
s => //The Set of falsy items
1.to(2) //Make a range [1, 2] to trim twice
./: //Fold over it,
(_) //starting with the list to trim
((a, _) => //The list a and the number, which is ignored
a.reverse //Reverse the list
dropWhile //And drop while
s) //Each item is present in s
s=>_.dropWhile(s).reverse.dropWhile(s).reverse
Boring.
f=lambda a,b:a[-1]in b and f(a[:-1],b)or a[0]in b and f(a[1:],b)or a
function(x,y,`+`=cumprod)x[!+x%in%y&!rev(+rev(x)%in%y)]
Finds matching elements (x %in% y) as vector of TRUE/FALSE values, and calculates the cumulative product (cumprod, re-assigned to + here to save bytes) to convert everything after the first FALSE to zero. Then does the same from the other end (by reversing x and the cumprod). Finally, negates (!) to select only the non-terminal-matching elements of x.
outer(x,y,'=='), didn't even think about %in%!
\$\endgroup\$
a,f=input()
for i in-1,0:
while a and a[i]in f:a.pop(i)
print a
The a and is necessary if the falsey list, f, contains all the elements of a and the completely stripped list will be empty. Without it, the program errors with IndexError: list index out of range.
Edit: -2 bytes thanks to Leo
‼(↔↓€
How?
↔↓€ removes the falsy elements from one end of the list, and then flips it:
↓ # drop the longest prefix of arg2 with elements that satisfy:
€ # are present in arg1
↔ # then reverse the result
So we just need to do this twice (to remove from both ends of the list, and to restore the list to its original orientation):
( groups ↔↓€ together (the parentheses are automatically closed at the end of the program), and the higher-order function ‼ runs a function provided as an argument twice.
t
A builtin that does exactly this. Works with multiple "falsey" values as well: Try it online!
Expects (a)(b), where a is the array to trim, using the values in the set b.
a=>b=>(g=a=>a.reverse().filter(i=c=>i|=!b.has(c)))(g(a))
#//.{e=#|##&@@#2,a___,e...}:>{a}&
-6 bytes and correction from @att
func[b t][while[find t b/1][take b]while[find t last b][take/last b]b]
parse, 123 bytesfunc[b t][r: copy[]foreach n t[append r reduce['quote n '|]]take/last r
parse b[remove some r to[any r end]remove some r]b]
m`^|$
,
(^)?,(([^,]+,)(?=.*¶.*,\3))*(¶.*)?(?(1)|$)
Try it online! Explanation:
m`^|$
,
Wrap both lists in additional commas.
(^)?,
Record whether this match is at the very start, but at the very least start at a comma.
(([^,]+,)(?=.*¶.*,\3))*
Match any number of terms which exist in the second array.
(¶.*)?
Optionally match the second array.
(?(1)|$)
If the match did not begin at the start, then it must end at the end.
Delete the matching values.
l->b->{while(b.contains(l.peek()))l.pop();while(b.contains(l.getLast()))l.pollLast();}
Uses a LinkedList as input/output.
Deque interface.
\$\endgroup\$
Apr 1, 2021 at 14:39
z(A)=length(A)
h(l,a,k)=\left\{l[a]=k:0,1\right\}
f(a,b)=\sum_{n=1}^{z(b)}(1-h(b,n,a))
s=f(A,B)
j(A,B)=A[\sum_{N=1}^{z(s)}N(1-h(s,N,0))\prod_{a=1}^{N-1}h(s,a,0)...z(A)]
p=j(A,B)
q=j(p[z(p)...1],B)
m(A,B)=q[z(q)...1]
Try It On Desmos!(Prettified Version)
Final function is \$m(a,b)\$, where \$a\$ is the list that is being trimmed, and \$b\$ is the list of "falsey" values that are trimmed from \$a\$.
Much harder than I initially anticipated because Desmos has limited list functionality. Hopefully it's fine if I output an one-element list with the one element being undefined([undefined]) when the output is supposed to be an empty list([]). If it isn't fine then tell me and I can fix(but it would cost more bytes ☹️)
Note: Not too sure why, but you can't directly paste the code into Desmos for some reason. You have to paste each expression one at a time in order for it to work.
=LET(x,A1#,r,ROW(x),y,IF(x>-1,r,""),FILTER(x,(r>=MIN(y))*(r<=MAX(y))))
jn m<rv.^dW<fe
To start we want to do the much simpler:
f x y=rv$dW(fe x)$rv$dw(fe x)y
This drops all things in x off the front, reverses it, then drops all things in x off the new front and reverses it back.
From here we can start by removing the y.
f x=rv<dW(fe x)<rv<dw(fe x)
Now we have the expression rv<dW(fe x) twice so let's fix that. jn will take a function on two arguments and pass the same value as both of its arguments.
f x=(rv<dW(fe x))<(rv<dW(fe x))
f x=jn m(rv<dW(fe x))
Now x is at the end so we can eta-reduce it away as well:
f x=jn m<rv.^dW<fe
Usually I would use Rv to reverse a list however .^ next to Rv breaks the Haskell parser, so I had to use rv instead. I've been aware of this danger for a while now and this was a pretty close call. I will probably rename .^ to <<.
"Compose a function with itself" achieved here with jn m is something that should probably have it's own name. It would have saved a byte here at least.
