NLP, Swift

Swift Trimming Trailing Punctuation

Lately, I’ve been working on a project that requires some basic MLP text processing to be performed on device.  A component of our text processing involved removing any trailing punctuation, no matter the language.

I’ve found the below String Extension is a good balance between effectiveness, performance, and readability.  Especially if you are collecting input from users prone to excessive punctuation.

 

Swift

Sentiment Analysis using Swift

Lately I’ve been working on several projects using conversational UI or “Bot” interactions.  A key interaction pattern when designing “Bots” you must listen to both the intent and sentiment of the text the user is providing.  Through the use of sentiment analysis you can help determine the mood of the user. This can be an important tool in determining when to offer help or involve a human.  You might think of this as the “help representative” moment we are all familiar with.  Using sentiment analysis you can try to offer help before that moment occurs.

There are several great sentiment analysis node.js packages but nothing I could find to run offline in Swift. A majority of the node.js projects seem to be a forks of the Sentiment package. The Sentiment-v2 package worked best for many of my cases and became my starting point.

A majority of the sentiment analysis  packages available through NPM use the same scoring approach. First they parse a provided phrase into individual words. For example “Cats are amazing” would be turned into an array of words, ie [“cats”, “are”,”amazing”].

Next a dictionary of keywords and associated weights are created. These scoring dictionary is created using the AFINN wordlist and Emoji Sentiment Ranking. In a nutshell, words like “amazing” would have a positive weight whereas words like “bad” would have a negative weight. The weight of each word in the provided phrase is added together to get the total weight of the phrase. If the phrase has a negative weight, chances are your user is starting to get frustrated or at least talking about a negative subject.

Using this approach I created the SentimentlySwift playground to demonstrate how this can be done on device using Swift.  This playground uses the same FINN wordlist and Emoji Sentiment Ranking weights to determine a sentiment analysis score without the network dependency.   To make comparisons easier, I tried to mirror the Sentiment package API as must as possible.  The below demonstrates the output for a few of the test phrases included with Sentiment.

Although the APIs are similar there is one important difference between the two approaches. The SentimentlySwift playground uses NSLinguisticTagger to tokenize the provided phrase. Using NSLinguisticTagger, SentimentlySwift first parsers each word into a series of word slices. Each slice is a word tokenized using the options provided to the NSLinguisticTagger. Next the slides are enumerated and an optional “tag” or word stem is calculated. For example, in the phrase “cats are amazing”, the “amazing” word generates a word stem of “amaze”. A better example would be the word “hiking” produces the word stem of “hike”.

The following snippet shows an example on how this can be implemented.

You might be asking why this is important? By implementing Lemmatisation you increase your AFINN hit rate and improve your overall analysis scoring.

This is one trick I’ve found for improving or at least monitoring your conversational UI or “Bot” interactions.

iOS, Swift

Thinking about Memory: Converting UIImage to Data in Swift

How often do you convert a UIImage into a Data object? Seems like a relatively straight forward task, just use UIImageJPEGRepresentation and your done.

After doing this I started seeing memory spikes and leaks appear which got me thinking on how I can better profile different options for performing this conversion. If you want to follow along you can create your own Swift Playground using this gist.

Approaches

The first step was looking at the different ways you can convert a UIImage into Data. I settled on the following three approaches.

UIImageJPEGRepresentation

Out of all the options this is the most straightforward and widely used. If you look at the testing blocks later in the post you can see I’m simply inlined the UIImageJPEGRepresentation with the test suite compression ratio.

UIImageJPEGRepresentation within an Autorelease Pool

Out of the box UIImageJPEGRepresentation provides everything we need. In some cases I’ve found it holds onto memory after execution. To determine if wrapping UIImageJPEGRepresentation in a autoreleasepool has any benefit I created the convenience method UIImageToDataJPEG2. This simply wraps UIImageJPEGRepresentation into a autoreleasepool closure as shown below. We later use UIImageToDataJPEG2 within our tests.

Using the ImageIO Framework

The ImageIO framework gives us a lower level APIs for working with images. Typically ImageIO has better CPU performance than using UIKit and other approaches. NSHipster has a great article with details here. I was interested to see if there was a memory benefit as well. The below helper function wraps the ImageIO functions into an API similar to UIImageJPEGRepresentation.  This makes testing much easier. Keep in mind you’ll need to have image orientation yourself.  For this example we just use Top, Left. If you are implementing yourself you’ll want read the API documentation available here.

What about UIImagePNGRepresentation?

UIImagePNGRepresentation is great when you need the highest quality image. The side effect of this is it has a largest Data size and memory footprint. This disqualified UIImagePNGRepresentation as an option for these tests.

Testing Scenarios

For my scenarios it was important to understand how memory is impacted based on the following:

  • Number of executions, i.e. what is the memory impact for calling an approach on one or many images.
  • How the Compression ratio impacts memory usage.

Image quality is an important aspect of my projects, so the tests where performed using the compression ratios of 1.0 and 0.9.  These compression ratios where then run using 1, 2, 14, 20, and 50 executions.  These frequencies demonstrate when image caching and Autorelease Pool strategies start to impact results.

Testing Each Approach

I test each of the above mentioned approaches using the template outlined below.  See the gist of the details for each approach.

  1. At the top of the method a memory sample is taken
  2. The helper method for converting a UIImage to a Data object is called in a loop.
  3. To make sure we are measure the same resulting data across tests, we record the length of the first Data conversion.
  4. When the loop has completed the proper number of iterations the memory is again sampled and the delta is recorded.

There is some variability on how each approach is tested.

The implementation for each approach is slightly different, but the same iteration and compression ratios are used to keep the outcome as comparative as possible.  Below is an example the strategy used to test the JPEGRepresentation with Autorelease Pool approach.

Test Results

Below is the result broken down by iteration.

Results for 1 Iteration

uiimagetodata-1

Results for 2 Iterations

uiimagetodata-2

Results for 14 Iterationsuiimagetodata-14

Results for 20 Iterations

UIImageToData-20.png

Results for 50 Iterations

uiimagetodata-50

Conclusion

I am sure there is a ton of optimizations that could be made to bring these numbers down. Overall the usage of UIImageJPEGRepresentation wrapped within an Autorelease Pool looks to be the best approach.  There is more work to be done on why the compression ratio has an inconsistent impact, my guess is this is a result to caching within the test.

Although the ImageIO strategy was better in a single execution scenario I question if the proper handling of image orientation would reduce or eliminate any of your memory savings.

Caveats

There are more comprehensive approaches out there. This is just an experiment using Playgrounds and basic memory sampling.  It doesn’t take into account any memory spikes that happen outside of the two sampling points or any considerations around CPU utilization.

Resources

  • Gist of the Swift Playground is available here
iOS, Swift

Stopping Tap Gesture from bubbling to child controls

The default behavior is for your tap or other gestures to bubble up to their child controls. This avoids the need to add a recognizer on all of your child controls. But this isn’t always the behavior you are looking for. For example imagine you create the below modal view. You want to add a tap gesture recognizer to the view itself so when your user taps the grey area it closes the modal. But you don’t want the gesture to be triggered when a tap is made on the content UIView of the modal.

modal-example

First adding the UITapGestureRecognizer

For our use case the first thing we need to do is add a UITapGestureRecognizer to the root UIView of the UIViewController. This will close our UIViewController when the grey area is tapped.

Limiting the scope of the Gesture

So that the UITapGestureRecognizer isn’t triggered when a tap is made to the content UIView we simply need to add protocol method to restrict the tap to the view it is associated with.

Putting it all together

Below is the full code associated with the modal UIViewController. If you are not familiar with how to create a modal UIViewController I would recommend checking out Tim Sanders tutorial here.

Swift

Swift excluding files from iCloud backup

Having your device automatically back-up to iCloud is one of the better services Apple provides.

Although not new, iCloud (introduced in June of 2011) back-up is one of the better services Apple has rolled out. If used right this removes a whole class of end user data lose fears.

However as an app developer you need to take this into consideration. Where it is privacy, size constraints, or other you need to be aware what you might be sending to iCloud.

You might wish to not back-up specific files. To do this you must set the file’s isExcludedFromBackup attribute to true. Below is a helper method to help get you started.

iOS, Swift

Check if GestureRecognizer added

One of my new projects dynamically generates a UI based on a DSL entered by the user. This leads to a host of defensive coding challenges since there is multiple code paths that can add controls and their associated gesture recognizers.

I found it helpful to add guard statements that stop recognizers from being added twice. The same approach is used for controls, but that is a different topic.

The below utility function can be used to check if the provided recognizer is already in the recognizer collection associated with an object.

The following code shows the utility function in action. All you have to do is incorporate containsGestureRecognizer into your guard statements.

Although really an edge case this was a fun bit of code to try out.

iOS, Swift

Removing CGPDFDocument Passwords

Working with PDFs on mobile is a pain. On the bright side at least Apple provides us CGPDFDocument

On the bright side Apple does provide CGPDFDocument. If you’re on Android you are left to 3rd party alternatives such as iText and PDFBox.

However examples on how to use CGPDFDocument are limited to the bare basics. On a recent project, I though I had a pretty basic requirement. Provide the user with the ability to remove the password for a protected PDF file. How hard could this be? Unfortunately I wasn’t able to find any examples on how to do this so decided to put my own together.

The most important thing you need to know about working with CGPDFDocument is it is immutable. This means you can’t just call unlockWithPassword and update a property to remove the password.

This means you will need to first unlock the PDF, then create an entirely new document. If you are working with large files you will need to be careful about the memory you are using. Instruments will be your best friend.

Let’s walk through an example. First we need to load a PDF file into a Data object as shown below.

Next you need to unlock your PDF using the existing password. In the example below we create a helper function called unlock that takes the Data from our PDF file and returns an unlocked CGPDFDocument. If the method is unable to either cast the Data object or unlock using the provided password a nil is returned.

We now have an unlocked CGPDFDocument object. Since this is immutable we need to use this as the source to create a new CGPDFDocument without a password. This is done by looping through the now unlocked CGPDFDocument and copying each CGPDFPage into a new CGPDFDocument. The copyPDFtoData helper function in the below example shows how the Core Graphics context is managed as part of the looping process. The end result is a Data object that is a copy of the PDF we started with, but without the password.

Keep in mind this isn’t an exact copy. The CGPDFDocument info and other meta data won’t be copied as part of this process. This can easily be added to the copyPDFtoData but was overkill for this example.

For convenience I’ve combined the above helper functions into a single class for easy maintenance and experimentation.

For more comprehensive PDF handling check out my PDFUtilities project.