aString := 'Now is the time for all good men to come to the aid of their blah blah blah'.

"inject: as select:"

aString inject: '' into: [:newString :nextCharacter |

newString , (nextCharacter isVowel ifTrue: [nextCharacter asString] ifFalse: [''])].

"--> 'oieieoaooeooeoeaioeiaaa'"