Run-length encoding (RLE)

Run-length encoding (RLE) is a very simple form of lossless data compression in which runs of data are stored as a single data value and count.

Encoder and decoder function showcase two kinds of conditional flow. Either type can be used for both jobs.
First case the values are prepared with conditions before a single call.
Second the condition is done first selecting between two calls of different values passes.

 Usage:

string1="hksdjfhkkkkdsfkljhriirenfcnlknd";
echo(RLEencode(string1));

string2="hhksdjfhkkkkdsfkljhriirenfcnlknd";
echo(RLEencode(string2));

string3=[0,1,1,2,2,2,2,1,1,0,-1,-1,-2,-2,-2,-2,-1,-1,0,1,1,2,2,2,2,1,1,0,-1,-1];
de=(RLEencode(string3));
echo(string3);
echo(de);
echo(RLEdecode(de));

function RLEencode(s,o,run=0,n=1)=
n==len(s)+1?o:
let(
newrun=s[n]==s[n-1]?run+1:0,
newo=s[n]==s[n-1]?o:concat(  o!=undef?o:[],[[run+1,s[ n-1]]])
)
RLEencode(s,newo,newrun,n+1)
;

function RLEdecode(s,o=[],run=1,n=-1)=
n==len(s)?o:
 let(next=[s[n][1]])
run ==1?

RLEdecode(s,concat(   o,next!=undef&&n>-1?next:[]),s[n+1][0],n+1)
:
RLEdecode(s,concat(   o,next!=undef?next:[] ),run-1,n);