Hi All, I was trying to figure an elegant way to slice strings (Python style), and came up empty. What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo? Craig
On 5/3/19 17:59, Craig Johnson wrote:
Hi All,
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I was trying to figure an elegant way to slice strings (Python style), and came up empty.
Â
What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo?
Â
Craig
You can use: 'Strings are intuitive' copyFrom: 4 to: 8 which should give you: 'ings '. There is an excellent tutorial about Strings on [1]. [1] http://stephane.ducasse.free.fr/FreeBooks/ByExample/14%20-%20Chapter%2012%20... If you share with us what are the results of your internet searchers to answer yourself while asking in this list and why they don't work for you, we can help you better (see [2], for a kind of updated classic on that). [2] http://www.catb.org/esr/faqs/smart-questions.html Cheers, Offray
As someone else already pointed out, the standard way to copy part of any array-like sequence is aSequence copyFrom: firstIncludedIndex to: lastIncludedIndex How could you have found this by yourself?
From the background, either Click-select Tools-select Playground or hold Ctrl down while typing OW (for Open Workspace). In the new Playground/workspace, type String then Ctrl-B. You now have a five-pane browser open on String.
About half way down the third panel on the top you will see converting copying displaying Click on copying. Guess what? You WON'T see anything that looks relevant! Maybe it's in an ancestral class. So look at the buttons under the top row of panes: All packages Scoped view | Flat Hier | Inst side Class side | ... Hier looks promising. Click it. Now in the second pane you will see ProtoObject Object Collection SequenceableCollection ArrayedCollection String ... Select the parent class, ArrayedCollection. Nope, nothing promising there either! Select the grandparent class, SequenceableCollection. And now the 'copying' method category has quite a few potentially interesting methods, including #copyFrom:to:. There are four other related methods that I would argue are in the wrong category: allButFirst allButFirst: count allButLast allButLast: count are in the 'accessing' category. If you want something a bit more flexible, you could add drop: d take: t "Discard the first |d| elements of the receiver if d >= 0. Discard the last |d| elements of the receiver if d <= 0. Return the first |t| elements of the result if t >= 0. Return the last |t| elements of the result if t <= 0. The result is the same kind of collection as the receiver." |lb ub n| n := self size. d abs >= n ifTrue: [^self copyEmpty]. d < 0 ifTrue: [lb := 1. ub := n + d] ifFalse: [lb := d+1. ub := n]. ub - lb + 1 <= t abs ifFalse: [ t < 0 ifTrue: [lb := ub + t + 1] ifFalse: [ub := lb + t - 1]]. ^self copyFrom: lb to: ub Now I would like to suggest that you not use anything like this *directly*. Go back to the Playground, and evaluate String with: (Character codePoint: 256) <Ctrl-P> The answer is 'Ä'. Pharo supports Unicode. Now try String with: $A with: (Character codePoint: 16r0304) In Pharo, the result looks like A followed by a separate macron, but when it's pasted into HTML it displays correctly as 'AÌ'. Pharo doesn't *quite* support Unicode. If it did, the two strings with different lengths and no codepoint in common would display exactly the same. The Unicode standard finds it necessary to distinguish between characters, glyphs, graphemes, grapheme clusters, codepoints, and a couple of other things. A Smalltalk String is a sequence of *codepoints*, not a sequence of "characters". There is no upper bound on the number of codepoints that may be needed to encode one "character" as the end user sees it, and from there on it gets *complicated*. For over 20 years, it hasn't really made sense to think of a string as a simply indexed sequence of characters. Integer indices are a useful implementation-level detail for remembering bounds from some "higher level" matching technique, but are much less useful than you might expect. On Wed, 6 Mar 2019 at 12:00, Craig Johnson <craig@hivemind.net> wrote:
Hi All,
I was trying to figure an elegant way to slice strings (Python style), and came up empty.
What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo?
Craig
Nice reply Richard - do you ever post any of these in a blog - the one below would be a great one to point to from Exercism...
On 6 Mar 2019, at 12:48, Richard O'Keefe <raoknz@gmail.com> wrote:
As someone else already pointed out, the standard way to copy part of any array-like sequence is aSequence copyFrom: firstIncludedIndex to: lastIncludedIndex
How could you have found this by yourself?
From the background, either Click-select Tools-select Playground or hold Ctrl down while typing OW (for Open Workspace). In the new Playground/workspace, type String then Ctrl-B. You now have a five-pane browser open on String.
About half way down the third panel on the top you will see converting copying displaying Click on copying.
Guess what? You WON'T see anything that looks relevant! Maybe it's in an ancestral class. So look at the buttons under the top row of panes: All packages Scoped view | Flat Hier | Inst side Class side | ... Hier looks promising. Click it.
Now in the second pane you will see ProtoObject Object Collection SequenceableCollection ArrayedCollection String ... Select the parent class, ArrayedCollection. Nope, nothing promising there either! Select the grandparent class, SequenceableCollection. And now the 'copying' method category has quite a few potentially interesting methods, including #copyFrom:to:.
There are four other related methods that I would argue are in the wrong category: allButFirst allButFirst: count allButLast allButLast: count are in the 'accessing' category.
If you want something a bit more flexible, you could add drop: d take: t "Discard the first |d| elements of the receiver if d >= 0. Discard the last |d| elements of the receiver if d <= 0. Return the first |t| elements of the result if t >= 0. Return the last |t| elements of the result if t <= 0. The result is the same kind of collection as the receiver." |lb ub n| n := self size. d abs >= n ifTrue: [^self copyEmpty]. d < 0 ifTrue: [lb := 1. ub := n + d] ifFalse: [lb := d+1. ub := n]. ub - lb + 1 <= t abs ifFalse: [ t < 0 ifTrue: [lb := ub + t + 1] ifFalse: [ub := lb + t - 1]]. ^self copyFrom: lb to: ub
Now I would like to suggest that you not use anything like this *directly*. Go back to the Playground, and evaluate
String with: (Character codePoint: 256) <Ctrl-P>
The answer is 'Ä'. Pharo supports Unicode. Now try
String with: $A with: (Character codePoint: 16r0304)
In Pharo, the result looks like A followed by a separate macron, but when it's pasted into HTML it displays correctly as 'AÌ'. Pharo doesn't *quite* support Unicode. If it did, the two strings with different lengths and no codepoint in common would display exactly the same.
The Unicode standard finds it necessary to distinguish between characters, glyphs, graphemes, grapheme clusters, codepoints, and a couple of other things. A Smalltalk String is a sequence of *codepoints*, not a sequence of "characters". There is no upper bound on the number of codepoints that may be needed to encode one "character" as the end user sees it, and from there on it gets *complicated*.
For over 20 years, it hasn't really made sense to think of a string as a simply indexed sequence of characters. Integer indices are a useful implementation-level detail for remembering bounds from some "higher level" matching technique, but are much less useful than you might expect.
On Wed, 6 Mar 2019 at 12:00, Craig Johnson <craig@hivemind.net <mailto:craig@hivemind.net>> wrote: Hi All,
I was trying to figure an elegant way to slice strings (Python style), and came up empty.
What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo?
Craig
In Calypso, select the checkbox next to the virtual category 'instance side', which will show all inherited methods (below Object) in the same browser, scroll to copy. #drop:take: sounds totally obscure to me, way worse than #copyFrom:to: first: or last: And what is your point with the Unicode rant ? What you are pointing at is called Normalization. It is not part of the standard image because the necessary databases and fonts are big. But is can be done in Pharo just fine. https://medium.com/concerning-pharo/an-implementation-of-unicode-normalizati... What is it with people complaining that they did not find something where they expected it ? Every language/environment/library/framework has a learning curve. The current class/method categorisations are what they are (historically and by design), there is more to life than string processing, many operations do make sense in other contexts too, that is a powerful thing.
On 6 Mar 2019, at 13:48, Richard O'Keefe <raoknz@gmail.com> wrote:
As someone else already pointed out, the standard way to copy part of any array-like sequence is aSequence copyFrom: firstIncludedIndex to: lastIncludedIndex
How could you have found this by yourself?
From the background, either Click-select Tools-select Playground or hold Ctrl down while typing OW (for Open Workspace). In the new Playground/workspace, type String then Ctrl-B. You now have a five-pane browser open on String.
About half way down the third panel on the top you will see converting copying displaying Click on copying.
Guess what? You WON'T see anything that looks relevant! Maybe it's in an ancestral class. So look at the buttons under the top row of panes: All packages Scoped view | Flat Hier | Inst side Class side | ... Hier looks promising. Click it.
Now in the second pane you will see ProtoObject Object Collection SequenceableCollection ArrayedCollection String ... Select the parent class, ArrayedCollection. Nope, nothing promising there either! Select the grandparent class, SequenceableCollection. And now the 'copying' method category has quite a few potentially interesting methods, including #copyFrom:to:.
There are four other related methods that I would argue are in the wrong category: allButFirst allButFirst: count allButLast allButLast: count are in the 'accessing' category.
If you want something a bit more flexible, you could add drop: d take: t "Discard the first |d| elements of the receiver if d >= 0. Discard the last |d| elements of the receiver if d <= 0. Return the first |t| elements of the result if t >= 0. Return the last |t| elements of the result if t <= 0. The result is the same kind of collection as the receiver." |lb ub n| n := self size. d abs >= n ifTrue: [^self copyEmpty]. d < 0 ifTrue: [lb := 1. ub := n + d] ifFalse: [lb := d+1. ub := n]. ub - lb + 1 <= t abs ifFalse: [ t < 0 ifTrue: [lb := ub + t + 1] ifFalse: [ub := lb + t - 1]]. ^self copyFrom: lb to: ub
Now I would like to suggest that you not use anything like this *directly*. Go back to the Playground, and evaluate
String with: (Character codePoint: 256) <Ctrl-P>
The answer is 'Ä'. Pharo supports Unicode. Now try
String with: $A with: (Character codePoint: 16r0304)
In Pharo, the result looks like A followed by a separate macron, but when it's pasted into HTML it displays correctly as 'AÌ'. Pharo doesn't *quite* support Unicode. If it did, the two strings with different lengths and no codepoint in common would display exactly the same.
The Unicode standard finds it necessary to distinguish between characters, glyphs, graphemes, grapheme clusters, codepoints, and a couple of other things. A Smalltalk String is a sequence of *codepoints*, not a sequence of "characters". There is no upper bound on the number of codepoints that may be needed to encode one "character" as the end user sees it, and from there on it gets *complicated*.
For over 20 years, it hasn't really made sense to think of a string as a simply indexed sequence of characters. Integer indices are a useful implementation-level detail for remembering bounds from some "higher level" matching technique, but are much less useful than you might expect.
On Wed, 6 Mar 2019 at 12:00, Craig Johnson <craig@hivemind.net> wrote: Hi All,
I was trying to figure an elegant way to slice strings (Python style), and came up empty.
What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo?
Craig
On Wed, 6 Mar 2019 at 12:00, Craig Johnson <craig@hivemind.net <mailto:craig@hivemind.net>> wrote:
What is the simplest way to copy characters between positions 4 and 8 from a string in Pharo?____
'1234567890' copyFrom: 5 to: 8 "5678" Page 207 in Updated Pharo by Example book explains more on substrings. HTH .. Subbu
From: Pharo-users [mailto:pharo-users-bounces@lists.pharo.org] On Behalf Of K K Subbu Sent: Wednesday, 06 March 2019 16:45 To: pharo-users@lists.pharo.org Subject: Re: [Pharo-users] Noob Question - slicing
'1234567890' copyFrom: 5 to: 8 "5678"
Page 207 in Updated Pharo by Example book explains more on substrings.
HTH .. Subbu
Thank you for this, it is perfectly clear. I disregarded the Pharo-by-Example linked from the Pharo.org page, because when I tried to use examples in that book to read text files, I found that the examples did not work under Pharo V7. The book is for Pharo 5. My mistake. If there's a later version of that book available, I'd love to know. Craig
participants (6)
-
Craig Johnson -
K K Subbu -
Offray Vladimir Luna Cárdenas -
Richard O'Keefe -
Sven Van Caekenberghe -
Tim Mackinnon