apl_in_the_shell

what

Dyalog APL in a docker container with a wrapper script that allows you to quickly use APL expressions/functions in your shell (in pipelines, etc.)

why

This got me thinking it would be fun to intersperse APL into my shell sessions.

The standard unix shell "primitives" might look arcane at first but once you learn them they are fantastic building blocks. The same is true for the APL primitives but the APL primitives are even more primitive, as you'll see in some examples below, so you can do things that aren't convenient to do with unix shell primitives.

how (build)

Have docker, make, and bash installed.

In a bash shell run:

make

how (use)

In a bash shell run:

alias apl='docker run --rm -i -v `pwd`:/mnt justin2004/apl_in_the_shell /home/containeruser/apl.sh'

On a Mac with ARM hardware (M1, M2, M3, etc.):

alias apl='docker run --platform linux/amd64 --rm -i -v `pwd`:/mnt justin2004/apl_in_the_shell /home/containeruser/apl.sh'

or put a file, called apl, with this content in one of the directories in your PATH:

#!/bin/bash
docker run --rm -i -v `pwd`:/mnt justin2004/apl_in_the_shell /home/containeruser/apl.sh "$@"

and make it executable.

Test to see if it is working:

apl --no-input  '⍳5'

should yield:

1 2 3 4 5

Most often we want to read from stdin or a file so that is why we needed to specify --no-input above to indicate that we just want to evaluate an expression with no other input.

If you don't specify --no-input or -ni then the process will wait for you to type something and press enter.

examples

How many users are running processes?

ps -e -o user= | sort -u | wc -l
13

ps -e -o user= | apl '≢∪'
13
ps -e -o user= | apl '≢∪' -
13
ps -e -o user= | apl '≢∪' /dev/stdin
13

Notice that reading from stdin is assumed so you don't have to specify it.

---

Generate a sequence of integers (one per line)

apl -ni '⍪⍳10'
 1
 2
 3
 4
 5
 6
 7
 8
 9
10

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

---

Generate 10 odd numbers

for (( i = 1; i < 20; i=i+2 )); do echo $i ; done
1
3
5
7
9
11
13
15
17
19

apl -ni '⍪¯1+2×⍳10'
 1
 3
 5
 7
 9
11
13
15
17
19

---

Histogram on process executable names and users running them

ps -e -o comm,user | sort | uniq -c | sort -nr  | head
     69 chrome          justin
     38 bash            justin
      8 docker          justin
      6 vi              justin
      6 containerd-shim root
      5 vim             justin
      5 ranger          justin
      4 java            root
      3 sh              justin
      3 kdmflush        root

ps -e -o comm,user | apl "{10↑v⌷⍨⊂⍒v←{⍺,⍨≢⍵}⌸⍵}"
69  chrome          justin
38  bash            justin
 9  docker          justin
 6  vi              justin
 6  containerd-shim root
 5  vim             justin
 5  ranger          justin
 4  java            root
 3  sh              justin
 3  kdmflush        root

You can also use two of Dyalog APL's General Utility Functions for rendering results: disp and display

To do this specify one of the rendering functions with -r (r as in render):

ps -e -o comm,user | apl -r disp "{5↑v⌷⍨⊂⍒v←{⍺,⍨≢⍵}⌸⍵}"
┌──┬──────────────────────┐
│41│chrome          justin│
├──┼──────────────────────┤
│34│bash            justin│
├──┼──────────────────────┤
│8 │vim             justin│
├──┼──────────────────────┤
│5 │vi              justin│
├──┼──────────────────────┤
│4 │sh              justin│
└──┴──────────────────────┘

ps -e -o comm,user | apl -r display "{5↑v⌷⍨⊂⍒v←{⍺,⍨≢⍵}⌸⍵}"
┌→────────────────────────────┐
↓    ┌→─────────────────────┐ │
│ 40 │chrome          justin│ │
│    └──────────────────────┘ │
│    ┌→─────────────────────┐ │
│ 34 │bash            justin│ │
│    └──────────────────────┘ │
│    ┌→─────────────────────┐ │
│ 8  │vim             justin│ │
│    └──────────────────────┘ │
│    ┌→─────────────────────┐ │
│ 5  │vi              justin│ │
│    └──────────────────────┘ │
│    ┌→─────────────────────┐ │
│ 4  │sh              justin│ │
│    └──────────────────────┘ │
└∊────────────────────────────┘

Putting a csv file in an ASCII table using ⎕CSV:

cat a.csv 
name,pet,age
bob,fido,33
fred,sam,10
jane,sal,3


apl -r disp --input-csv "⊢" a.csv
┌────┬────┬───┐
│name│pet │age│
├────┼────┼───┤
│bob │fido│33 │
├────┼────┼───┤
│fred│sam │10 │
├────┼────┼───┤
│jane│sal │3  │
└────┴────┴───┘

The --input-csv (or -ic) option is equivalent to:

apl -ni -r disp "⎕CSV 'a.csv'"

Note we specify --no-input (-ni) there because the csv file name is specified inside the APL expression (as a character vector) and not as one of the command line arguments.

---

Transpose a csv file:

cat a.csv | apl --output-csv -ic '⍉'
name,bob,fred,jane
pet,fido,sam,sal
age,33,10,3

cat a.csv | apl -r disp -ic '⍉'
┌────┬────┬────┬────┐
│name│bob │fred│jane│
├────┼────┼────┼────┤
│pet │fido│sam │sal │
├────┼────┼────┼────┤
│age │33  │10  │3   │
└────┴────┴────┴────┘

Notice above that --output-csv (or -oc) prints csv to stdout. If you don't specify --output-csv Dyalog APL's matrix rendering would be used.

---

Add an id column to a csv file:

apl -oc -ic "{⍵,⍨(⊂'id'),⍳¯1+≢⍵}" a.csv
id,name,pet,age
1,bob,fido,33
2,fred,sam,10
3,jane,sal,3

The awk solution isn't bad:

awk -v OFS="," 'NR==1{print "id",$0} {print NR,$0}' a.csv
id,name,pet,age
1,name,pet,age
2,bob,fido,33
3,fred,sam,10
4,jane,sal,3

But since awk isn't csv aware (which matters if you have quoted cells with the delimiter character in them) it can't easily handle the general case where you might want to put the id column somewhere in the middle:

apl -oc -ic "{2⌽⍵,⍨(⊂'id'),⍳¯1+≢⍵}" a.csv
pet,age,id,name
fido,33,1,bob
sam,10,2,fred
sal,3,3,jane

Of course column ordering of csv is mostly meaningless but I've seen cases where it matters.

---

If you want to use the column names in csv files use the -ch (or --use-csv-headers) option:

cat some.csv
name,weight
opal,62
owen,65
justin,195

apl -ch -ic "{⍵[;name]}" some.csv
┌────┬────┬──────┐
│opal│owen│justin│
└────┴────┴──────┘

apl -ch -ic  "{⍵[;weight]}" some.csv
62 65 195

# sum of all the weights
apl -ch -ic  "{+/⍵[;weight]}" some.csv
322

# average of the weights
cat some.csv | apl  -ch -ic  "{(+/÷≢)⍵[;weight]}"
107.3333333

Note that the column names that are available are just the leading alpha characters (upper and lower case). So if you have a column name "Name on business card" the column will be simply "Name". "Name4you" will be "Name".

Also note when you use this option the header row is dropped.

---

Putting the /etc/passwd file in an ASCII table (inspired by this):

head -2 /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin

apl -r disp "{↑':'(≠⊆⊢)¨⍵}" /etc/passwd
┌─────────────┬─┬─────┬─────┬──────────────────────────────────┬─────────────────┬─────────────────┐
│root         │x│0    │0    │root                              │/root            │/bin/bash        │
├─────────────┼─┼─────┼─────┼──────────────────────────────────┼─────────────────┼─────────────────┤
│daemon       │x│1    │1    │daemon                            │/usr/sbin        │/usr/sbin/nologin│
├─────────────┼─┼─────┼─────┼──────────────────────────────────┼─────────────────┼─────────────────┤
│bin          │x│2    │2    │bin                               │/bin             │/usr/sbin/nologin│
├─────────────┼─┼─────┼─────┼──────────────────────────────────┼─────────────────┼─────────────────┤
...

---

Get 10 random words from the dictionary file

head -400 /usr/share/hunspell/en_US.dic | tail -5
Amie/M
Amiga/M
Amish/M
Amman/M
Amoco/M

cat /usr/share/hunspell/en_US.dic | apl "{↑v/¨⍨~∨\¨'/'=v←⍵[10?⍴⍵]}"
Kewpie
Jarlsberg
Delphinus
Nepal
Priceline
Khazar
Emmy
Lillie
Alba
Dropbox

cat /usr/share/hunspell/en_US.dic | shuf | head -10 | sed -e 's,/.*,,'
Okefenokee
Meyers
merited
prude
migrate
occultist
spotter
swift
murmurer
adopt

---

Just some dyadic examples

cat nums.txt
1
2
3
4

echo -e 'one\ntwo\nthree\nfour' | apl "{⍺}" nums.txt -
 1  2  3  4

echo -e 'one\ntwo\nthree\nfour' | apl "{⍵}" nums.txt -
 one  two  three  four

echo -e 'one\ntwo\nthree\nfour' | apl "{⍎¨⍺}" nums.txt -
1 2 3 4

echo -e 'one\ntwo\nthree\nfour' | apl "{+/⍎¨⍺}" nums.txt -
10

echo -e 'one\ntwo\nthree\nfour' | apl "{⍺ ⍵}" nums.txt -
  1  2  3  4    one  two  three  four

echo -e 'one\ntwo\nthree\nfour' | apl "{(⍎¨⍺)∘.⍴⍵}" nums.txt -
 o     t     t     f
 on    tw    th    fo
 one   two   thr   fou
 oneo  twot  thre  four

echo -e 'one\ntwo\nthree\nfour' | apl -r disp "{(⍎¨⍺)∘.⍴⍵}" nums.txt -
┌────┬────┬────┬────┐
│o   │t   │t   │f   │
├────┼────┼────┼────┤
│on  │tw  │th  │fo  │
├────┼────┼────┼────┤
│one │two │thr │fou │
├────┼────┼────┼────┤
│oneo│twot│thre│four│
└────┴────┴────┴────┘

entering APL glyphs

I use this approach on Linux. You run that single command mentioned there. Then you'll be able to use your keyboard's right Alt key as a modifier to enter APL characters. For instance, you enter can the iota character ⍳ by pressing the right Alt + i, the rho character ⍴ by pressing the right Alt + r and so on.

Also see here for other input methods.

I sometimes use this vim input approach as well.

similar projects

For q there is awq.

For j there is this.

jacinda "APL meets AWK"

NOTES

Dyalog APL is free for non-commercial use. See here for license details.

Dyalog APL is running in a docker container with your host's PWD bindmounted into the container at the container's PWD. If you reference a file name it must use relative (from your PWD) paths. So you can't reference files above your host PWD. And you can't .. to get above your host's PWD.