Filtering lists

Keep what matches

filter goes through a list and keeps only the lines that match a pattern. In a pattern, * stands for any run of characters (or none) and ? for exactly one:

put "apple" & return & "banana" & return & "cherry" & return & "avocado" into tFruit
filter tFruit with "a*"
put tFruit

apple
avocado

without does the opposite, and throws the matches away:

put "apple" & return & "banana" & return & "cherry" & return & "avocado" into tFruit
filter tFruit without "a*"
put tFruit

banana
cherry

Wildcard patterns

The pattern must match the whole line. Put * on both sides to find lines that contain something anywhere:

put "x1" & return & "y22" & return & "x333" & return & "box" into tCodes
filter tCodes with "x?" into tShort
put tShort
filter tCodes with "*x*" into tAnyX
put tAnyX

x1
x1
x333
box

into puts the result in another variable and leaves the list as it was, so you can filter the same list several ways. Square brackets match one of a set of characters: [aeiou]* keeps lines that start with a vowel.

Items, and empty lines

Say items of to filter a comma-separated list. A very common job is dropping the blank lines from text: filter it without empty.

put "cat,dog,cow,horse" into tAnimals
filter items of tAnimals with "c*"
put tAnimals
put "one" & return & return & "two" & return & return & "three" into tText
filter tText without empty
put tText

cat,cow
one
two
three

Filtering with regular expressions

For patterns a wildcard cannot say, filter with a regular expression. Unlike a wildcard, a regular expression matches anywhere in the line unless you anchor it with ^ (the start) or $ (the end). The lesson Regular expressions teaches the language of these patterns.

put "alpha" & return & "beta" & return & "gamma" & return & "delta" into tWords
filter tWords with regex pattern "^[ab]"
put tWords
put "order 66" & return & "no number" & return & "room 101" into tLines
filter tLines with regex pattern "[0-9]+$"
put tLines

alpha
beta
order 66
room 101

Removing duplicates

Filtering cannot see whether a line has appeared before, but an array can: each value becomes a key, and a key can only be there once. split with as set does exactly that, and the keys gives the list back. The keys of an array come in no particular order, so sort them:

put "pear" & return & "fig" & return & "pear" & return & "apple" & return & "fig" into tList
split tList by return as set
put the keys of tList into tUnique
sort lines of tUnique
put tUnique

apple
fig
pear

Arrays are the subject of the next two lessons.

put "notes.txt,cat.png,song.mp3,beach.jpg,apple.png" into tFiles
replace comma with return in tFiles
filter tFiles with regex pattern "\.(png|jpg)$"
sort tFiles
put tFiles

apple.png
beach.jpg
cat.png