Re: Nested list comprehension

[cdunn2001]

I don't see "collect" used in that comprehension module at all. Also, 
**comprehension** is slightly broken with nim-1.0.0. I haven't tried nim-devel 
yet. (I can only use official releases at work.)

Re: Nested list comprehension

[Araq]

You can always follow our github instructions to produce a Nim devel version.

First get Nim from github:

git clone 
[https://github.com/nim-lang/Nim.git](https://github.com/nim-lang/Nim.git)  
cd Nim  
build_all.bat   

Re: Nested list comprehension

[andrewgohlk]

I'm using MSYS2/MINGW64, so can't use choosenim. :(

Re: Nested list comprehension

[dawkot]

As I said, you must use the devel version. You can install it with a tool 
called choosenim.

Re: Nested list comprehension

[andrewgohlk]

Hi, I encountered "Error: undeclared identifier: 'collect'"

Re: Nested list comprehension

[dawkot]

I generally only put brackets where neccessary.

You can write this using devel version of nim (you can use choosenim) 


import tables, sugar, sets, sequtils

proc cross(xs, ys: string): seq[string] =
  for x in xs: (for y in ys: result.add x & y)

let
  rows = "ABCDEFGHI"
  cols = "123456789"
  squares = cross(rows, cols)

let unitSeq =
  collect(newSeq, for c in cols: cross(rows, $c)) &
  collect(newSeq, for r in rows: cross($r, cols)) &
  collect(newSeq,
for rs in ["ABC", "DEF", "GHI"]:
  for cs in ["123", "456", "789"]:
cross(rs, cs))

let units = collect newOrderedTable:
  for s in squares:
{s: collect(newSeq, for u in unitSeq: (if s in u: u))}

let peers = collect newOrderedTable:
  for s in squares:
var v = units[s].foldl(a & b)
v.delete v.find s
{s: v}

echo "unitSeq:"; for u in unitSeq: echo u
echo "\nunits"; for k, v in units: echo k, ": ", v
echo "\npeers"; for k, v in peers: echo k, ": ", v


Run

For some reason peers isn't what it should, but the rest is ok.

Re: Nested list comprehension

[didlybom]

It would be nice if when something is deprecated in the standard library there 
was a link to the associated discussion/decision summary (if any). I found the 
deprecated list comprehension type a while ago and was curious about why it was 
deprecated.

Re: Nested list comprehension

[whospal]

Expected results... 


# Python output:
unitlist = [['A1', 'B1', 'C1', 'D1', 'E1', 'F1', 'G1', 'H1', 'I1'],
['A2', 'B2', 'C2', 'D2', 'E2', 'F2', 'G2', 'H2', 'I2'],
['A3', 'B3', 'C3', 'D3', 'E3', 'F3', 'G3', 'H3', 'I3'], ['A4', 'B4', 'C4', 
'D4', 'E4', 'F4', 'G4', 'H4', 'I4'], ['A5', 'B5', 'C5', 'D5', 'E5', 'F5', 'G5', 
'H5', 'I5'], ['A6', 'B6', 'C6', 'D6', 'E6', 'F6', 'G6', 'H6', 'I6'], ['A7', 
'B7', 'C7', 'D7', 'E7', 'F7', 'G7', 'H7', 'I7'], ['A8', 'B8', 'C8', 'D8', 'E8', 
'F8', 'G8', 'H8', 'I8'], ['A9', 'B9', 'C9', 'D9', 'E9', 'F9', 'G9', 'H9', 
'I9'], ['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9'], ['B1', 'B2', 
'B3', 'B4', 'B5', 'B6', 'B7', 'B8', 'B9'], ['C1', 'C2', 'C3', 'C4', 'C5', 'C6', 
'C7', 'C8', 'C9'], ['D1', 'D2', 'D3', 'D4', 'D5', 'D6', 'D7', 'D8', 'D9'], 
['E1', 'E2', 'E3', 'E4', 'E5', 'E6', 'E7', 'E8', 'E9'], ['F1', 'F2', 'F3', 
'F4', 'F5', 'F6', 'F7', 'F8', 'F9'], ['G1', 'G2', 'G3', 'G4', 'G5', 'G6', 'G7', 
'G8', 'G9'], ['H1', 'H2', 'H3', 'H4', 'H5', 'H6', 'H7', 'H8', 'H9'], ['I1', 
'I2', 'I3', 'I4', 'I5', 'I6', 'I7', 'I8', 'I9'], ['A1', 'A2', 'A3', 'B1', 'B2', 
'B3', 'C1', 'C2', 'C3'], ['A4', 'A5', 'A6', 'B4', 'B5', 'B6', 'C4', 'C5', 
'C6'], ['A7', 'A8', 'A9', 'B7', 'B8', 'B9', 'C7', 'C8', 'C9'], ['D1', 'D2', 
'D3', 'E1', 'E2', 'E3', 'F1', 'F2', 'F3'], ['D4', 'D5', 'D6', 'E4', 'E5', 'E6', 
'F4', 'F5', 'F6'], ['D7', 'D8', 'D9', 'E7', 'E8', 'E9', 'F7', 'F8', 'F9'], 
['G1', 'G2', 'G3', 'H1', 'H2', 'H3', 'I1', 'I2', 'I3'], ['G4', 'G5', 'G6', 
'H4', 'H5', 'H6', 'I4', 'I5', 'I6'], ['G7', 'G8', 'G9', 'H7', 'H8', 'H9', 'I7', 
'I8', 'I9']]

Run

Re: Nested list comprehension

[whospal]

Expected results... 


# Python output:
unitlist = [['A1', 'B1', 'C1', 'D1', 'E1', 'F1', 'G1', 'H1', 'I1'],
['A2', 'B2', 'C2', 'D2', 'E2', 'F2', 'G2', 'H2', 'I2'],
['A3', 'B3', 'C3', 'D3', 'E3', 'F3', 'G3', 'H3', 'I3'], ['A4', 'B4', 'C4', 
'D4', 'E4', 'F4', 'G4', 'H4', 'I4'], ['A5', 'B5', 'C5', 'D5', 'E5', 'F5', 'G5', 
'H5', 'I5'], ['A6', 'B6', 'C6', 'D6', 'E6', 'F6', 'G6', 'H6', 'I6'], ['A7', 
'B7', 'C7', 'D7', 'E7', 'F7', 'G7', 'H7', 'I7'], ['A8', 'B8', 'C8', 'D8', 'E8', 
'F8', 'G8', 'H8', 'I8'], ['A9', 'B9', 'C9', 'D9', 'E9', 'F9', 'G9', 'H9', 
'I9'], ['A1', 'A2', 'A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9'], ['B1', 'B2', 
'B3', 'B4', 'B5', 'B6', 'B7', 'B8', 'B9'], ['C1', 'C2', 'C3', 'C4', 'C5', 'C6', 
'C7', 'C8', 'C9'], ['D1', 'D2', 'D3', 'D4', 'D5', 'D6', 'D7', 'D8', 'D9'], 
['E1', 'E2', 'E3', 'E4', 'E5', 'E6', 'E7', 'E8', 'E9'], ['F1', 'F2', 'F3', 
'F4', 'F5', 'F6', 'F7', 'F8', 'F9'], ['G1', 'G2', 'G3', 'G4', 'G5', 'G6', 'G7', 
'G8', 'G9'], ['H1', 'H2', 'H3', 'H4', 'H5', 'H6', 'H7', 'H8', 'H9'], ['I1', 
'I2', 'I3', 'I4', 'I5', 'I6', 'I7', 'I8', 'I9'], ['A1', 'A2', 'A3', 'B1', 'B2', 
'B3', 'C1', 'C2', 'C3'], ['A4', 'A5', 'A6', 'B4', 'B5', 'B6', 'C4', 'C5', 
'C6'], ['A7', 'A8', 'A9', 'B7', 'B8', 'B9', 'C7', 'C8', 'C9'], ['D1', 'D2', 
'D3', 'E1', 'E2', 'E3', 'F1', 'F2', 'F3'], ['D4', 'D5', 'D6', 'E4', 'E5', 'E6', 
'F4', 'F5', 'F6'], ['D7', 'D8', 'D9', 'E7', 'E8', 'E9', 'F7', 'F8', 'F9'], 
['G1', 'G2', 'G3', 'H1', 'H2', 'H3', 'I1', 'I2', 'I3'], ['G4', 'G5', 'G6', 
'H4', 'H5', 'H6', 'I4', 'I5', 'I6'], ['G7', 'G8', 'G9', 'H7', 'H8', 'H9', 'I7', 
'I8', 'I9']]

Run

Re: Nested list comprehension

[whospal]

Thanks for the info. Yes, I'd tried the sugar package but failed. Will checkout 
the comprehension package.

Re: Nested list comprehension

[whospal]

Thanks!

Just a clarification, why your codes have the brackets around the y loop, and 
not around the result.add?


 cross(xs, ys: string): seq[string] =
  for x in xs: (for y in ys: result.add x & y)

Run

While @trtt has it around the result.add?


 cross(a, b: string): seq[string] =
  for ac in a:
for bc in b:
  result.add(ac & bc)

Run

This is some of the syntax that confuse me.

Re: Nested list comprehension

[kaushalmodi]

> how about you first get familiar with the correct Nim syntax for them? link

Wait, you are linking against the deprecated lc syntax.

I believe the closest non-deprecated solution is 
[https://github.com/alehander92/comprehension](https://github.com/alehander92/comprehension)
 ?

Re: Nested list comprehension

[miran]

> The documentation of Seq & Tables are very poor in Nim. Not many examples to 
> learn from.

If something has a solid documentation and lots of examples, then it is 
`tables` module. :rolleyes:

Re: Nested list comprehension

[miran]

> I tried with...
> 
> [invalid syntax]

If you really want to force list comprehensions, how about you first get 
familiar with the correct Nim syntax for them? 
[link](https://nim-lang.org/docs/sugar.html#\[\].m%2CListComprehension%2Cuntyped%2Cuntyped)

But my advice would be: don't use list comprehensions in Nim — think about how 
would you have written your python code without them and then try to translate 
_that_ version, you'll have much better time.

Re: Nested list comprehension

[dawkot]

This should work: 


import tables, strutils

proc cross(xs, ys: string): seq[string] =
  for x in xs: (for y in ys: result.add x & y)

let
  rows = "ABCDEFGHI"
  cols = "123456789"
  squares = cross(rows, cols)

var unitSeq: seq[string]
for c in cols: unitSeq.add cross(rows, $c)
for r in rows: unitSeq.add cross(cols, $r)
for rs in ["ABC", "DEF", "GHI"]: (for cs in ["123", "456", "789"]: 
unitSeq.add cross(rs, cs))

var units, peers: Table[string, seq[string]]
for s in squares:
  var tmp: seq[string]
  for u in unitSeq: (if s in u: tmp.add u)
  units[s] = tmp
  if (let i = tmp.find s; i >= 0): tmp.del i
  peers[s] = tmp


Run

Re: Nested list comprehension

[whospal]

Some more codes...


# Python codes:
unitlist = ([cross(rows, c) for c in cols] +
[cross(r, cols) for r in rows] +
[cross(rs, cs) for rs in ('ABC','DEF','GHI') for cs in 
('123','456','789')])

units = dict((s, [u for u in unitlist if s in u])
for s in squares)

peers = dict((s, set(sum(units[s],[]))-set([s]))
for s in squares)


Run

I tried with... 


 # Nim codes:
var unitlist: seq[string] =
[for c in cols: cross(rows, cast[string](c))] +
[for r in rows: cross(r, cols)] +
[for rs in ("ABC","DEF","GHI"):
for cs in ("123","456","789"):
cross(rs, cs)]

var units = initTable[string](4):
for s in squares:
for u in unitlist:
if s in u:
{s, u}

var peers = initTable[string](4):
for s in squares:
{s, toHashSet(sum(units[s],[]))-toHashSet([s])


Run

But encountered lots of exceptions... :(

The documentation of Seq & Tables are very poor in Nim. Not many examples to 
learn from.

Please help!

Re: Nested list comprehension

[whospal]

@trtt & @miran, Thanks very much. Yes, i notice I made the mistake of the 
return type in the proc. 

Re: Nested list comprehension

[miran]

There are few problems with your Nim version, e.g. returning `string` instead 
of `seq[string]` (cause this is what the Python version does - it returns a 
list).

Here is a correct Nim version: 


proc cross(xs, ys: string): seq[string] =
  ## Cross product of elements in A and elements in B.
  for x in xs:
for y in ys:
  result.add x


Run

Re: Nested list comprehension

[trtt]

That's not list comprehension in nim, you just iterated over two strings and 
then joined the elements without using them.


proc cross(a, b: string): seq[string] =
  for ac in a:
for bc in b:
  result.add(ac & bc)

let digits = "123456789"
let letters = "ABCDEFGHI"
echo  cross(letters, digits)


Run

Nested list comprehension

[whospal]

Hi, I'm new to Nim-lang.

I wanted to convert a Python script to Nim to improve my understanding of Nim.

I have the following Python code: 


# Python codes:
def cross(A, B):
"""Cross product of elements in A and elements in B."""
return [a+b for a in A for b in B]

digits   = '123456789'
rows = 'ABCDEFGHI'
cols = digits
squares  = cross(rows, cols)


Run

I tried to convert to Nim code but failed: 


# Nim codes:
proc cross(A: string, B: string): string =
## Cross product of elements in A and elements in B.
result = string:
for a in A:
for b in B:
a

let digits   = "123456789"
let rows = "ABCDEFGHI"
let cols = digits

var squares  = cross(rows, cols)


Run

I hit " Error: expression 'a & b' is of type 'string' and has to be discarded"

Please help to explain how to convert the nested list comprehension. Thanks in 
advance.