# A list of number modulus their indices in the list

A simple one: Take a list of positive integers as input and output the numbers modulus their 1-based index in the list.

If the input integers are {a, b, c, d, e, f, g} then the output should be {a%1, b%2, c%3, d%4, e%5, f%6, g%7} where % is the modulus operator.

Test cases:

10  9  8  7  6  5  4  3  2  1
0  1  2  3  1  5  4  3  2  1

8 18  6 11 14  3 15 10  6 19 12  3  7  5  5 19 12 12 14  5
0  0  0  3  4  3  1  2  6  9  1  3  7  5  5  3 12 12 14  5

1
0

1  1
0  1


($[1..]).zipWith mod  Try it online! A trick to flip I learned from a golf of Anders Kaseorg. # Operation Flashpoint scripting language, 73 bytes f={l=_this;r=[];i=0;while{i<count l}do{r=r+[(l select i)%(i+1)];i=i+1};r}  Call with: numList = [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]; hint format["%1\n%2", numList, numList call f];  Output: • What... this is a thing? – JAD Jun 15 '17 at 12:35 • @JarkoDubbeldam Yes. The game allows players to create their own scenarios, and there is an in-game scripting language designed to supplement mission designing. However, since the language is Turing-complete, you can do pretty much whatever you want with it. – Steadybox Jun 15 '17 at 13:22 # Python 2, 35 bytes i=1 for x in input():print x%i;i+=1  Try it online! Counts the index up manually, as per a tip of mine. • If you can exit with an error (I forget if that's the default) you can shave a couple bytes. – FryAmTheEggman Jun 14 '17 at 22:39 # Jelly, 2 bytes %J  Try it online! Explanation: %J J List 1 .. len(input). This is results in a list of the indexes. % Modulo.  Basically, the code modulos the original list by the list of indexes. • As soon as I saw this question, I thought "that's %J in Jelly, I wonder if anyone has answered with that answer?". I guess someone else had the same idea :-D – user62131 Jun 14 '17 at 21:49 • @ais523 You think you were the only one? Think again! – Erik the Outgolfer Jun 15 '17 at 9:10 # R, 24 18 bytes pryr::f(x%%seq(x))  Evaluates to the function: function (x) x%%seq(x)  Which uses seq_along() to create a vector of the same length as x, starting at 1, and then %% to take the modulo. Default behaviour of seq when presented with a vector is seq(along.with = x) which is the same output as seq_along(x), but 6 bytes shorter. • seq(x) is a handy thing to have around, since I'm always using 1:length(x). – Giuseppe Jun 15 '17 at 14:08 • @Giuseppe Yeah I was kinda surprised as well. – JAD Jun 15 '17 at 14:13 # R, 27 bytes x=scan();cat(x%%1:sum(1|x))  saved 5 bytes thanks to @Jarko saved 4 more thanks to @Giuseppe saved 2 more thanks to @Taylor Scott Saved 2 more thanks to @returnbull • 35 it is - removed unneeded last paren – Zahiro Mor Jun 15 '17 at 13:47 • you don't need the ' ' (space) at the end of cat; that's the default separator – Giuseppe Jun 15 '17 at 13:51 • you can drop 2 bytes to get 33 by reducing this down to x<-scan();cat(x%%1:length(x)," ") -- oh and a couple formatting tips, 1) you only need 4 spaces to the left of your code for it to be properly indented and marked 2) you can add a <!-- language-all: lang-r --> flag before your code to have it be highlighted (though this changes little in this example) 3) you do not need the brakets around your language's name 4) oh and you don't need to make a comment when you make edits to a post – Taylor Scott Jun 15 '17 at 13:57 • (1) You can use = instead of <- to save a byte. (2) The specification says "output" rather than "print", so you can probably drop the cat(), saving 5 bytes. (3) sum(1|x) is one byte shorter than length(x). – rturnbull Jun 16 '17 at 13:51 # APL (Dyalog), 5 bytes ⍳∘≢|⊢  Try it online! ⍳ the indices ∘ of ≢ the length of the argument | that modulus ⊢ the argument • Always amazed that a "mainstream" language can be so economical. The APL way seems naturally to be code golf: e.g. (~T∊T∘.×T)/T←1↓⍳R ⍝ primes up to R or life←{↑1 ω∨.∧3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂ω} ⍝ Game of Life – user15259 Jun 14 '17 at 22:27 • @YiminRong You can do better: Primes to R: (⊢~∘.×⍨)1↓⍳R and GoL (in Version 16.0): K∊⍨⊢∘⊂⌺3 3 where K is a constant. – Adám Jun 14 '17 at 22:31 • @YiminRong Try the primes finder here! – Adám Jun 14 '17 at 22:32 # Cubix, 19 bytes ;ww.1I!@s%Ow;)Sow.$


Try it online!

    ; w
w .
1 I ! @ s % O w
; ) S o w . $. . . . .  Watch It Run A fairly straight forward implementation. • 1 push 1 to the stack to start the index • I!@ get the integer input and halt if 0 • s%Ow swap the index up, mod, output result and change lane • ;) remove result and increment index • Sow push 32, output space and change lane (heading down from o) • $O jump the output
• w;w change lange, remove 32 from stack and change lane onto the I input

# 05AB1E, 2 bytes

ā%

ā  # Push the range(1, len(a) + 1)
% # Mod each element in the input by the same one in this list

• Interesting, I thought it'd be like DgL%, nice. – Magic Octopus Urn Jun 16 '17 at 21:07
• @carusocomputing I originally had gL% because I forgot about ā. – Riley Jun 16 '17 at 21:57
• mind going a bit more in-depth on ā for me? I believe I've never used it is it just like for each but in a 1 to n+1 manner like vy<code>}) but implied vy<code>})? – Magic Octopus Urn Jun 16 '17 at 21:58
• @carusocomputing it pushes an array with values 1 to the length of the popped array. It's equivalent to gL. TIO – Riley Jun 16 '17 at 22:04
• Does it also dupe the input? Or is implicit input now extended automatically to the closest available input? – Magic Octopus Urn Jun 16 '17 at 22:06

## Mathematica, 22 bytes

#&@@@Mod~MapIndexed~#&


One more Mathematica approach.

• MapIndexed@Mod is almost good enough :'( – ngenisis Jun 14 '17 at 22:39

# Starry, 75 70 bytes

      +  , + +   *    +  + +      +*   +    *  .               + + .'


Try it online!

### Explanation

This is an infinite loop that keeps reading numbers from the input and increasing a counter initiallized at 1. For each pair of input and counter, the modulus is computed and printed.

To end the loop when input has been exhausted, the following trick is used. When no more input is available, trying to read one more number gives a 0. Thus, we divide the read number by itself, and if it is 0 the program ends with an error. Else we discard the result and continue.

      +              Push 1. This is the initial value of the counter
Mark label
,                  Read number from input and push it. Gives 0 if no more input
+                   Duplicate top of the stack
+                   Duplicate top of the stack
*                 Pop two numbers and push their division. Error if divisor is 0
+                Pop (discard) top of the stack
+                  Swap top two numbers
+                   Duplicate top of the stack
+              Push 1
*                    Pop two numbers and push their sum. This increases the counter
+                 Rotate stack down, to move increased counter to bottom
*                Pop two numbers and push their modulus
.                  Pop a number and print it as a number
+     Push 10
+                   Duplicate top of the stack
.                   Pop a number (10) and print it as ASCII character (newline)
'                    If top of the stack is non-zero (it is, namely 10) go to label


# MATL, 4, 3 bytes

tf\


Try it online!

One byte saved thanks to @LuisMendo!

# Brachylog, 9 bytes

l⟦₁;?↔z%ᵐ


Try it online!

### Explanation

l⟦₁          [1, ..., length(Input)]
;?↔z      Zip the Input with that range
%ᵐ    Map mod


# Japt, 5 4 bytes

®%°T


Try it

## Explanation

     :Implicit input of array U
®    :Map over the array
%    :Modulo of the current element
°T   :T (0, initially) incremented by 1

• I think you can save a byte with ®%°T (actually, you could still use Y there if you wanted) – ETHproductions Jun 15 '17 at 11:00
• Aha. Thanks, @ETHproductions. – Shaggy Jun 15 '17 at 11:02

# R, 22 bytes

pryr::f(x%%1:sum(x|1))


R performs 1:length(x) before doing the modulus.

• Nice find with sum(x|1)! – JAD Jun 15 '17 at 12:51
• Just found out that using seq() instead of seq_along() does the same thing. So that is a few bytes shorter again. – JAD Jun 15 '17 at 13:02
• I was going to tell you that, but I didn't have the rep to comment. Glad you figured it out. – Shayne03 Jun 15 '17 at 13:12

# Python 2, 42 bytes

lambda l:[v%(i+1) for i,v in enumerate(l)]


Try it online!

• You can remove the space before the for – Beta Decay Jun 14 '17 at 21:19
• 41 bytes: lambda l:[v%-~i for i,v in enumerate(l)] – ovs Jun 14 '17 at 21:24
• Or, lambda l:[v%i for i,v in enumerate(l,1)]. – xnor Jun 14 '17 at 21:26

zipWith(flip mod)[1..]


Try it online!

Also: flip(zipWith mod)[1..].

# Mathematica, 21 bytes

#~Mod~Range@Length@#&


Try it online!

or 20 bytes (by Martin)

#~Mod~Range@Tr[1^#]&

• Tr[1^#] for Length@#. – Martin Ender Jun 14 '17 at 21:33
• that one doesn't work on mathics, so I'm keeping them both – J42161217 Jun 14 '17 at 21:40
• You are missing a # as the second last character in your first answer. – Ian Miller Jun 15 '17 at 0:26

# Excel VBA, 59 46 Bytes

### Golfed

Anonymous VBE Immediate window funtion that takes a space ( ) delimited array string as input from range [A1] and output the numbers modulus their 1-based index in the starting list to the VBE immediate window

For Each n In Split([A1]):i=i+1:?n Mod i;:Next


Input / Output:

[A1]="10 9 8 7 6 5 4 3 2 1" ''# or manually set the value
For Each n In Split([A1]):i=i+1:?n Mod i;:Next
0  1  2  3  1  5  4  3  2  1


### Old Subroutine version

Subroutine that takes input as a passed array and outouts to the VBE immediate window.

Sub m(n)
For Each a In n
i=i+1
Debug.?a Mod i;
Next
End Sub


Input / Ouput:

m Array(10,9,8,7,6,5,4,3,2,1)
0  1  2  3  1  5  4  3  2  1


### Ungolfed

Option Private Module
Option Compare Binary
Option Explicit
Option Base 0 ''# apparently Option Base 1 does not work with ParamArrays

Public Sub modIndex(ParamArray n() As Variant)
Dim index As Integer
For index = LBound(n) To UBound(n)
Debug.Print n(index) Mod (index + 1);
Next index
End Sub


Input / Output:

Call modIndex(10,9,8,7,6,5,4,3,2,1)
0  1  2  3  1  5  4  3  2  1


# CJam, 9 bytes

{_,,:).%}


Anonymous block that expects an array on the stack and replaces it by the output array.

Try it online!

### Explanation

{       }    e# Define block
_           e# Duplicate
,          e# Length
,         e# Range, 0-based
:)       e# Add 1 to each entry
.%     e# Vectorized modulus


# J, 9 bytes

>:@i.@#|[


1 ... n | original list

| is mod

# JavaScript (ES6), 22 bytes

a=>a.map((x,y)=>x%++y)


{print $1%NR}  # tcl, 35 lmap l$L {puts [expr \$l%[incr i]]}


# GNU APL 1.2, 9 bytes

(⍳⍴R)|R←⎕


APL operates from right to left, hence the parentheses.

R←⎕ assigns user input to vector R.

⍴R gives the length of the vector; ⍳⍴R gives a vector with all numbers from 1 to that length (so the indices).

| is the mod operator (a|b yields b%a). APL operates on arrays, so the code snippet a vector containing each element from the user's input mod its index.

# Pari/GP, 22 bytes

a->[a[n]%n|n<-[1..#a]]


Try it online!

# Pyth, 5

.e%bh

    hk     # 1-based index of (implicit) lambda variable
b       # element
%        # element mod (1-based index)
.e    Q    # enumerated map over (implicit) input


# Octave, 19 bytes

@(n)mod(n,1:nnz(n))


Try it online!

An anonymous function that takes n as input, and performs element-wise modulus with the list 1, 2, 3.

# Braingolf, 18 bytes

V1R&,{v.m1+v%}&,=;


Try it online!

## Explanation

V1R&,{v.m1+v%}&,=;  Implicit input from commandline args
&,               Reverse stack1
{.......}      Foreach loop, runs for each item in stack1
v             Switch to stack2
.m           Duplicate last item on stack and move duplicate to stack1
1+         Increment last item on stack
v%       Return to stack1, pop last 2 items and push modulus result
&,    Reverse stack1
=   Output stack1
;  Suppress implicit output


# Java 8 / C#, 39 bytes

a->{for(int i=0;i<a.length;a[i]%=++i);}


Try it here.

Also works in C# by replacing -> with => and length with Length:

a=>{for(int i=0;i<a.Length;a[i]%=++i);}


Try it here.

Explanation:

a->{                       // Method with integer-array parameter and no return-type
for(int i=0;i<a.length;  //  Loop over the indexes of the array (0-indexed)
a[i]%=++i            //   And replace every integer with itself mod (1+i)
);                       //  End of loop
}                          // End of method


Modifies the input-array, hence the lack of a return.

• Essentially what I'd do in C# +1, could also comment about it working for C# too if you change -> to => and capitaliselength. – TheLethalCoder Jun 15 '17 at 8:22