# Linear Regression on a String

This challenge is a little tricky, but rather simple, given a string s:

meta.codegolf.stackexchange.com


Use the position of the character in the string as an x coordinate and the ascii value as a y coordinate. For the above string, the resultant set of coordinates would be:

0, 109
1, 101
2, 116
3, 97
4, 46
5, 99
6, 111
7, 100
8, 101
9, 103
10,111
11,108
12,102
13,46
14,115
15,116
16,97
17,99
18,107
19,101
20,120
21,99
22,104
23,97
24,110
25,103
26,101
27,46
28,99
29,111
30,109


Next, you must calculate both the slope and the y-intercept of the set you've garnered using Linear Regression, here's the set above plotted: Which results in a best fit line of (0-indexed):

y = 0.014516129032258x + 99.266129032258


Here's the 1-indexed best-fit line:

y = 0.014516129032258x + 99.251612903226


f("meta.codegolf.stackexchange.com") = [0.014516129032258, 99.266129032258]


Or (Any other sensible format):

f("meta.codegolf.stackexchange.com") = "0.014516129032258x + 99.266129032258"


Or (Any other sensible format):

f("meta.codegolf.stackexchange.com") = "0.014516129032258\n99.266129032258"


Or (Any other sensible format):

f("meta.codegolf.stackexchange.com") = "0.014516129032258 99.266129032258"


Just explain why it is returning in that format if it isn't obvious.

Some clarifying rules:

- Strings are 0-indexed or 1 indexed both are acceptable.
- Output may be on new lines, as a tuple, as an array or any other format.
- Precision of the output is arbitrary but should be enough to verify validity (min 5).


This is lowest byte-count wins.

• Do you have any link / formula to calculate the slope and the y-intercept? – Rod Jan 9 '17 at 17:56
• Dear Unclear-voters: While I agree that it is nice to have the formula, it is by no means necessary. Linear regression is a well-defined thing in the mathematical world, and the OP may want to leave finding the equation up to the reader. – Nathan Merrill Jan 9 '17 at 18:02
• en.wikipedia.org/wiki/Simple_linear_regression – Magic Octopus Urn Jan 9 '17 at 18:11
• Is it okay to return the actual equation of the best-fit line, such as 0.014516129032258x + 99.266129032258? – Greg Martin Jan 9 '17 at 18:18
• This challenge's title has put this wonderful song in my head for the rest of the day – Luis Mendo Jan 9 '17 at 21:09

# MATL, 8 bytes

n:G3$1ZQ  1-based string indexing is used. Try it online! ### Explanation n: % Input string implicitly. Push [1 2 ... n] where n is string length. % These are the x values G % Push the input string. A string is an array of chars, which is % equivalent to an array of ASCII codes. These are the y values 3$     % The next function will use 3 inputs
1      % Push 1
ZQ     % Fit polynomial of degree 1 to those x, y data. The result is an
% array with the polynomial coefficients. Implicitly display


# Octave, 292624 20 bytes

@(s)s/[!!s;1:nnz(s)]


Try it Online!

We have the model

y= intercept *x^0 + slope * x
= intercept * 1  + slope * x


Here y is the ASCII value of string s

To find parameters intercept and slope we can form the following equation:

s = [intercept slope] * [1 X]


so

[intercept slope] = s/[1 x]


!!s converts a string to a vector of ones with the same length as the string.
The vector of ones is used for estimation of the intercept.
1:nnz(s) is range of values from 1 to number of elements of the string used as x.

@(s)ols(s'+0,[!!s;1:nnz(s)]')


For test paste the following code into Octave Online

(@(s)ols(s'+0,[!!s;1:nnz(s)]'))('meta.codegolf.stackexchange.com')


A function that accepts a string as input and applies ordinary least squares estimation of model y = x*b + e

The first argument of ols is y that for it we transpose the string s and add with number 0 to get its ASCII code.

• /, great idea! – Luis Mendo Jan 9 '17 at 20:06

# TI-Basic, 51 (+ 141) bytes

Strings are 1-based in TI-Basic.

Input Str1
seq(I,I,1,length(Str1->L1
32+seq(inString(Str2,sub(Str1,I,1)),I,1,length(Str1->L2
LinReg(ax+b)


Like the other example, this outputs the equation of the best fit line, in terms of X. Also, in Str2 you need to have this string, which is 141 bytes in TI-Basic:

!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_abcdefghijklmnopqrstuvwxyz{|}~ The reason this cannot be a part of the program is because two characters in TI-Basic cannot be automatically added to a string. One is the STO-> arrow, but this is not a problem because it is not a part of ASCII. The other is the string literal ("), which can be stringified only by typing into a Y= equation and using Equ>String(. • I was seriously wondering if anyone would bust out their old calculators for this :). I had my old TI-83 in mind when I thought this up. – Magic Octopus Urn Jan 9 '17 at 19:08 • @carusocomputing Hey, nice! I like the TI-Basic programming language a lot and I use it for many of my code golfs. If only it supported ASCII... – Timtech Jan 9 '17 at 21:13 • Two comments: 1, you can stringify " by prompting for it as user input in a program as well, which doesn't help you here, but I just wanted to point that fact out. 2, I don't recognize some of those characters as existing on the calculator. I could be wrong, but for example, where do you get @ and ~? As well as #, $, and &. – Patrick Roberts Jan 10 '17 at 10:57
• Thanks for the comment, @PatrickRoberts. Those are two-byte tokens starting with 0xBB. Look in Column D of tibasicdev.wikidot.com/miscellaneous-tokens – Timtech Jan 10 '17 at 23:07

## R, 46 45 bytes

x=1:nchar(y<-scan(,""));lm(utf8ToInt(y)~x)$co  Reads input from stdin and for the given test case returns (one-indexed): (Intercept) x 99.25161290 0.01451613  • Slightly shorter (but untested, possibly some evaluation problems in parsing the formula): lm(utf8ToInt(y<-scan(,""))~1:nchar(y))$co – rturnbull Jan 10 '17 at 15:16
• @rturnbull I tried this at first but it seems like the x variable has to be pre-defined for lm to work. – Billywob Jan 10 '17 at 15:17
• @rturnbull I get a variable lengths differ error on that. We are given s so x=1:nchar(s);lm(charToRaw(s)~x)$co saves some bytes. I also don't know if the $co is technically necessary, as you still get the intercept + coefficient without it – Chris Jan 10 '17 at 15:18
• @Chris Fairly sure that is not a viable answer. There should be some input from stdin or as a function argument. – Billywob Jan 10 '17 at 15:24
• Fair enough, just my reading of the question - it gives a more fair comparison to the python + octave answers as well – Chris Jan 10 '17 at 15:27

# Python, 82 80 bytes

-2 bytes thanks to @Mego

Using scipy:

import scipy
lambda s:scipy.stats.linregress(range(len(s)),list(map(ord,s)))[:2]

• Unnamed lambdas are allowed, so you can drop the f=. – Mego Jan 9 '17 at 20:15
• @DigitalTrauma numpy.linalg.lstsq apparently differs in arguments to scipy.stats.linregress and is more complex. – dfernan Jan 9 '17 at 21:09

# Mathematica, 31 bytes

Fit[ToCharacterCode@#,{1,x},x]&


Unnamed function taking a string as input and returning the actual equation of the best-fit line in question. For example, f=Fit[ToCharacterCode@#,{1,x},x]&; f["meta.codegolf.stackexchange.com"] returns 99.2516 + 0.0145161 x.

ToCharacterCode converts an ASCII string to a list of the corresponding ASCII values; indeed, it defaults to UTF-8 more generally. (Kinda sad, in this context, that one function name comprises over 48% of the code length....) And Fit[...,{1,x},x] is the built-in for computing linear regression.

• Thanks for the example of the 1-indexed line, didn't have to calculate it because of you haha. – Magic Octopus Urn Jan 9 '17 at 19:19

# Node.js, 84 bytes

Using regression:

s=>require('regression')('linear',s.split.map((c,i)=>[i,c.charCodeAt()])).equation


## Demo

// polyfill, since this is clearly not Node.js
function require(module) {
return window[module];
}
// test
["meta.codegolf.stackexchange.com"].forEach(function test(string) {
console.log(string);
console.log(this(string));
},
// submission
s=>require('regression')('linear',s.split.map((c,i)=>[i,c.charCodeAt()])).equation
);
<script src="https://cdn.rawgit.com/Tom-Alexander/regression-js/master/src/regression.js"></script>

## Sage, 76 bytes

var('m','c')
y(x)=m*x+c
f=lambda x:find_fit(zip(range(len(x)),map(ord,x)),y)


Hardly any golfing, probably longer than a golfed Python answer, but yeah...

# J, 11 bytes

3&u:%.1,.#\


This uses one-based indexing.

Try it online!

## Explanation

3&u:%.1,.#\  Input: string S
#\  Get the length of each prefix of S
Forms the range [1, 2, ..., len(S)]
1,.    Pair each with 1
3&u:         Get the ASCII value of each char in S
%.       Matrix divide


# JavaScript, 151 148 bytes

s=>([a,b,c,d,e]=[].map.call(s,c=>c.charCodeAt()).reduce(([a,b,c,d,e],y,x)=>[a+1,b+x,c+x*x,d+y,e+x*y],[0,0,0,0,0]),[k=(e*a-b*d)/(c*a-b*b),(d-k*b)/a])


function f(s) {
var [n, sx, sx2, sy, sxy] = [].map.call(s, c => c.charCodeAt(0))
.reduce(([n, sx, sx2, sy, sxy], y, x) => [
n + 1,
sx + x,
sx2 + x * x,
sy + y,
sxy + x * y
], [0, 0, 0, 0, 0]);
var k = (sxy * n - sx * sy) / (sx2 * n - sx * sx);
return [k, (sy - k * sx) / n];
}

$(() =>$('#run').on('click', () => console.log(f($('#input').val())))); <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <textarea id="input" style="width: 100%">meta.codegolf.stackexchange.com</textarea> <button id="run">Run</button> • You can save a byte by removing 0 from c.charCodeAt(0), and another 2 bytes by moving the k=... comma group and putting it directly in first index of the returned array like [k=...,(d-k*b)/a] – Patrick Roberts Jan 10 '17 at 10:41 # Javascript (ES6), 112 bytes s=>[m=(a=b=c=d=0,([...s].map((u,x)=>{a+=n=x,b+=y=u.charCodeAt(),c+=x*x,d+=x*y}),++n)*d-a*b)/(n*c-a*a),b/n-m*a/n]  F=s=>[m=(a=b=c=d=0,([...s].map((u,x)=>{a+=n=x,b+=y=u.charCodeAt(),c+=x*x,d+=x*y}),++n)*d-a*b)/(n*c-a*a),b/n-m*a/n] const update = () => { console.clear(); console.log(F(input.value)); }; input.oninput = update; update(); #input { width: 100%; box-sizing: border-box; } <input id="input" type="text" value="meta.codegolf.stackexchange.com" length=99/> <div id="output"></div> # Haskell, 154 142 bytes import Statistics.LinearRegression import Data.Vector g x=linearRegression(generate(Prelude.length x)i)$i.fromEnum<$>fromList x i=fromIntegral  It is far too long for my likings because of the imports and long function names, but well. I couldn't think of any other Golfing method left, although I'm not expert on the area of golfing imports. Stripped 12 bytes by replacing ord and the import of Data.Char by fromEnum thanks to nimi. • You can replace ord with fromEnum and get rid of import Data.Char. – nimi Jan 10 '17 at 23:48 # SAS Macro Language, 180 bytes Uses 1-based indexing. The solution gets to be pretty wordy when the output is only the slope and intercept. %macro t(a);data w;%do i=1 %to %length(&a);x=&i;y=%sysfunc(rank(%substr(&a,&i,1)));output;%end;run;proc reg outtest=m;model y=x/noprint;run;proc print data=m;var x intercept;%mend;  ## Clojure, 160 bytes No built-ins, uses the iterative algorithm described at Perceptron article. Might not converge on other inputs, in that case lower the learning rate 2e-4 and maybe increase the iteration count 1e5. Not sure if the non-iterative algorithm would have been shorter to implement. #(nth(iterate(fn[p](let[A apply e(for[x(range(count %))](-(int(get % x))(*(p 1)x)(p 0)))](mapv(fn[p e](+(* e 2e-4)p))p[(A + e)(A +(map *(range)e))])))[0 0])1e5)  Example: (def f #( ... )) (f "meta.codegolf.stackexchange.com") [99.26612903225386 0.014516129032464659]  ## Maple, 65 bytes Statistics:-LinearFit(b*x+a,[$(1..length(s))],convert(s,bytes),x)


Usage:

s := "meta.codegolf.stackexchange.com";
Statistics:-LinearFit(b*x+a,[\$(1..length(s))],convert(s,bytes),x);


Returns:

99.2516129032259+0.0145161290322573*x


Notes: This uses the Fit command to fit a polynomial of the form a*x + b to the data. The ASCII values for the string are found by converting to bytes.