DEV Community: Juan De Dios Santos

RowSwift: A Simple CSV Analyzer for iOS

Juan De Dios Santos — Fri, 12 Sep 2025 21:28:12 +0000

I’ve published my first iOS app and would like to write a few words about it.

It’s called RowSwift, a CSV analyzer designed to give you quick answers and visualizations in just a few taps.

Why I Built It

The idea came to me after a three-week trip where I ran out of mobile data. Stuck with a CSV file on my phone, I wanted to count rows, calculate a standard deviation, and create a histogram of one of its columns. Numbers, Apple’s spreadsheet app, was an option, but I’ll admit: my spreadsheet skills are quite bad. And without internet on the go, I couldn’t just search “how to calculate the standard deviation of column three.”

Back home (after examining the CSV using the R programming language), I thought: what if I learn the basics of iOS development and Swift to build something that does exactly that? A little and quick tool for rows, stats, and histograms. “Little” and “quick” were key: I wanted something that could load a file and get me what I needed in minutes.

That toy project grew into something bigger. At some point, I told myself: Why not polish it and publish it? So here we are, with the first version of the app and a CSV file I’d still like to analyze.

From Rows to Insights

RowSwift makes it easy to get started. You can paste data, load a file from your device, read it from a URL, or try one of the sample datasets (like the classic Iris flowers).

For this walkthrough, I used a CSV statement from a month when I barely touched my credit card. As soon as the file loads, you are presented with the row and column count, along with a preview of the first rows neatly displayed as tiles. A quick filter bar at the top helped me zero in on transactions, and a long press on any row allowed me to copy it as CSV, JSON, or even key-value pairs. Handy if I need to send details elsewhere.

But the real fun began when I moved into the Visualizations tab.

Visualizing Spending

I began by creating a histogram of my transaction amounts. With adjustable bins and the option to choose between relative frequency and percentages, it quickly became clear that most of my purchases were under $27. That lined up with my memory: a handful of small, forgettable swipes.

RowSwift also summarizes each numeric column with quick statistics, such as the mean and standard deviation. For my spending that month, the average was $24.40 with a standard deviation of $34. Not terrible.

To dig deeper, I switched over to the grouping tab. By organizing transactions by category, I could see how much I spent on groceries, restaurants, transportation, and, the obvious winner, shopping. The culprit? Pokémon cards. Not surprised.

Still, the most frequent category wasn’t shopping but restaurants, with over 50% of the transactions bearing this label. The pie chart below confirms it. What the data doesn’t say (unless you look at the actual merchant) is that, in reality, these entries were mostly from the bakeries and coffee shops that provided me the sweet boost I craved while coding the app.

What’s Next?

RowSwift was born from a simple curiosity and an interest in learning something new. Honestly, I never expected to have so much fun building it. Now that it’s live on the App Store, I plan to continue adding in practical techniques from the data world, including more statistics such as median and grouped standard deviation, richer charts, and diverse export options.

At the time of writing, the app is free to use and does not contain any ads.

Learnings

Way too many.

As someone with limited mobile development experience (and none at all on iOS), diving into a new language and the intricacies of Apple’s ecosystem was both cool and frustrating.

One of the biggest challenges? UI and UX design. Being an iPhone user didn’t mean I knew how to design for iOS. Once I decided to upgrade the project from “just a toy” to a real app, I hit a wall. I started sketching ideas on paper. Didn’t help; too abstract and no colors. Then I tried using Canva and similar design tools, but all the clicking got in the way. Eventually, I went back to something more familiar: Photoshop. I designed a tile-based layout that reminded me of my earliest days building apps for Windows 8. It felt right. Translating that design into SwiftUI was the next step.

Coding with SwiftUI went better than expected. Yes, there was a lot of Googling, a lot of poring over documentation, and many long conversations with ChatGPT to sanity-check ideas, ask whether I was following best practices, solve bugs, and help me understand error messages—thinking of “The compiler is unable to type-check this expression in reasonable time” still haunts me. However, once I wrapped my head around a few NavigationStack, things started to click.

The real beast was creating the charts. That was a different level of frustration. Half the time, I wasn’t even sure if what I wanted to do was possible in the framework. And just when I thought I was done—plot complete, interactions working (yay!)—I decided to add chart exporting. That’s when I (and the app) almost broke. Sizes were wrong, colors were off, font was too small, and data was missing. It was a disaster. But somehow, it all came together, and I was able to finish it.

Which brings me to marketing. The app is done… now what? I didn’t plan that far ahead. I’m still figuring this part out. I built this for the challenge, learning, and to count CSV rows. But of course, I’d love it if the app ended up helping someone else, too.

I’m not sure how I’ll get the word out just yet, but maybe this write-up is a good first step.

You can download RowSwift at https://apps.apple.com/us/app/rowswift/id6749399145.

For more information, visit https://rowswift.com.

Analyzing My Reddit Usage: a data-driven approach to achieving my New Year’s Resolution of reducing my online time

Juan De Dios Santos — Wed, 22 Feb 2023 00:32:06 +0000

One of my new year's resolutions was to spend less time online. This includes time on Reddit—despite my love for the website. Gone are the days when I went through several websites to get the latest news about my favorite topics. Now, I rely on Reddit’s algorithm to feed me the content I need as I scroll down. However, I’ve found myself scrolling too much, and I knew I had to take some action.

With January behind us, I decided to investigate whether I had successfully cut down my Reddit usage for this month compared to January 2022. To investigate this, I turned to RescueTime, a software I use to track my online activity. While the platform provides a dashboard with helpful insights that could answer my question, I exported the data and used the R programming language to conduct a deeper analysis that explores how much time I spent on various subreddits and how my habits changed.

Reddit. Photo by me.

The dataset

RescueTime’s dataset consists of one row per page viewed and five columns. Of these, only three were relevant to this experiment:

Date: The date when I visited the page.
Time Spent (seconds): How much time I spent on the visited page.
Activity: The title of the visited page.

The screenshot below presents two of the dataset’s rows. The first row is a 1002 seconds long visit to Reddit’s main page on January 13, and the second is a 24 seconds long visit to the PKMNTCGDeals subreddit on January 13.

Two rows of the dataset.

I can use the content from the activity column to identify whether the entry corresponds to a visit to Reddit’s main page or a page viewed on a subreddit.

For example, the string "Reddit - Dive into anything” (seen in the screenshot’s first row) is a visit to the main page, and the pattern “colon followed by a term,” where “term” is the subreddit (seen in the screenshot’s second row, e.g., “: PKMNTCGDeals”), is a page viewed on that subreddit. To tailor the dataset to my needs, I wrote a couple of regexes to extract the subreddit's name, removed entries corresponding to visits to the settings and user's pages (to leave the rows denoting visits to the actual content), and filtered out rows representing subreddits that I visited fewer than five times.

The analysis

I spent 13.51 hours on Reddit in January 2022. During this time, I visited 90 different subreddits and Reddit’s main page. The latter saw the most activity, with 4.65 hours amassed from 94 visits. Then, there’s the Formula 1 subreddit, or r/formula1 in Reddit-speech, with 1.22 hours and 86 visits, and Ask Reddit, with 0.88 hours accumulated across 31 visits. Figure 1 shows the top 10 frequented subreddits (including the main page).

Figure 1. Hours spent on Reddit in January, 2022.

In January 2023, I spent 7.39 hours on Reddit—that’s 54% less time than last year— yay me! In Figure 2, you can find the top 8 subreddits I have visited the most during this time. Why 8 and not 10? That’s because by then, I had only visited eight subreddits more than five times.

Figure 2. Hours spent on Reddit in January, 2023.

Comparing both charts shows that the frequented subreddits have changed. For some reason, “Next Fucking Level” (a subreddit that shows people doing incredible and cool things) was last month’s second most-seen section of Reddit, while Formula 1 is nowhere to be seen. This isn’t because I don’t like Formula 1 anymore, but because this year’s winter break has been slow and not newsworthy. Another detail I noticed is that Pokémon Masters, a mobile game, is also not there because I finally stopped playing it after almost three years (I miss it, though). However, another Pokémon-related subreddit, “PKMNTCGDeals,” or Pokémon Trading Card Game Deals, has taken its place, for I started playing and collecting Pokémon cards last year and am always on the lookout for good prices.

Knowing that the time on Reddit has decreased, I wanted to know what day of the week was affected the most. Was it a weekday or during the weekend? Figure 3 reveals it.

Figure 3. Difference in hours, broken down by the day of the week.

Thursdays and Sundays are the two days that benefited the most. You might wonder why these two days and what’s the connection (if there is any). The answer is that these are the two days I play Pokémon in my local league—which also explains why PKMNTCGDeals is now one of my newest favorite subreddits.

Final words

I spent 50% less time on Reddit in January 2023 than in January 2022 due to my new year’s resolution to reduce my online time. This change was also influenced by hobbies I started or abandoned last year. For example, I stopped playing the mobile game Pokémon Masters, which led to a decrease in visits to its subreddit. Conversely, my newfound interest in the Pokémon Trading Card Game led to frequent the PKMNTCGDeals more often.

In terms of days, Thursdays and Sundays saw the largest change, with significantly less time spent on Reddit. Now, I’m using this gained time to pursue other activities such as watching Formula 1 (once the season starts), playing Pokémon, and writing articles like this.

This won’t be the only update I’ll do regarding my goal, as I plan to repeat this analysis at the end of each quarter to ensure I’m achieving my goal. Until then, happy (moderately) browsing!

I gave a talk at my alma mater and loved it

Juan De Dios Santos — Fri, 10 Feb 2023 19:29:19 +0000

I gave a talk at my alma mater and loved it. Said place is the University of Puerto Rico, Rio Piedras Campus, where I did my bachelor’s in Computer Science over ten years ago. The original idea (and why my professors invited me) was to talk to the students about my current position as a Trust and Safety Software Engineer, my studies abroad, and some of the projects I’ve done over the years. However, I gave it a slight twist. I wanted this talk to be personal and to resonate among the students. I wanted it to be memorable since I would present it at a place I love and to an audience I could relate to. So I decided that besides talking about my professional career so far (which I consider having started on my first day of college), I wanted to cover lessons I’ve learned, my achievements, and my regrets.

As I stood in the front of a room that for years I knew from the backseats and vocalized my slideshow, I realized that I would have loved to hear such a talk back when I was a student. Being there felt like coming full circle. I was no longer a student but a professional wanting to share a bit of knowledge and motivation with the 30-plus pair of eyes that were looking at me. Of everything I discussed, three points stood out the most: networking, that it’s ok to change interest, and being vocal. These were points the students asked about, the professors agreed with, and I could reflect upon them as I presented them. With the presentation still fresh in my mind, I want to write about what I discussed to save it for posterity.

I owe much of my career to networking. My first professional experience (an internship I did abroad) came to me thanks to a professor who recommended me. Two years later, during my last year of university, my college buddy, which I’ll call C, had just finished her internship and asked me if I wanted to backfill her position. I said yes, she put in a good word for me, and I got in. This role involved developing application prototypes for clients, and it was one of these clients who gave me my first full-time software developer position as soon as my internship contract ended. During my presentation, I told the students that now, their best contacts are the peers sitting next to them. These are the people with whom they will share years of lessons. In that time, they will collaborate and compete with each other, do extracurricular activities, share frustrations, and most importantly, learn about each other strengths, weaknesses, likes, dislikes, and professional goals—making them the voice that will vouch for them as C did for me.

The first slide

While at college, I didn’t know what path I wanted to follow—surely not a career in the Trust & Safety field. Heck, I didn’t even know what that was. But back then, I was obsessed with video games, so the thought of building the next AAA games sounded fantastic and intriguing. Or so it did until I started toying with game development and faced the harsh truth that I wasn’t enjoying it. So, I moved over to app development in the Windows environment (which was the focus of my second internship). And it was alright; I didn’t dislike it and didn’t love it. But I wanted to love it, or at least to love something. Thus, I read a lot and thought of my favorite courses from the university. The courses that popped up in my mind involved math and data. That combination of programming while dealing with numbers and information sounded great (plus, at that time, the terms “big data” and “data mining” were becoming popular). And that’s how I risked it all and went abroad to do a Master’s degree focusing on that. Now, it’s been a couple of years since I finished my Master’s, and I’m happily working as a Trust & Safety Software Engineer in a role that involves a lot of programming, numbers, and data. Will I be doing this forever? Probably not. At some point, my interests will change, and I’ll be ok with it. As a student, this thought was haunting and scary; now, it is adventurous.

I ended the presentation by talking about being vocal, for which I meant to share and expose your work. Many of my extracurricular professional activities have been a byproduct of a project or article I have previously made public. For example, in 2021, I published a book after being approached by an editor from a publishing house. The editor, whose name I’ll forever cherish, emailed me a short message saying he found an article of mine and invited me to write a book covering the same framework. Having your work out there is similar to having a buddy who can vouch for you. The only difference is that, unlike a person, your work will always be accessible. But I’m not saying this is easy, for I understand the fear and doubts that come with having your name and content on the internet. Even after all these years, I read my articles five times before clicking “publish,” check my sources before commenting, and sweat while standing in front of an audience out of fear of mispronouncing a word—which happens all the time, like that day I gave a talk at my alma mater (and I loved it).

Dear Random Forest

Juan De Dios Santos — Mon, 08 Jul 2019 04:31:45 +0000

Dear random forest, my name’s Juan, a huge fan.

Lately, I’ve been thinking a lot about you, wondering how you are feeling, and pondering about what the future has for you. You see, I’m sad that the sound of your leaves rustling is not being heard the way it used to. Since some years ago, your other fans and practitioners decided to leave the trails of your forest in exchange for a more neural and networked life. And while I’m sure they had their reasons, this makes me sad. Let me tell you something.

Photo by Sebastian Unrau on Unsplash

When I started to learn about machine learning, I had difficulties understanding many of the essential concepts that are part of our beloved field. Oh, my friend, yes. You have no idea. However, my luck turned when I met your youngest sibling, the decision tree, whom I call Detri.

Back then, through Detri, I learned the bases and essential concepts I so desperately needed. I have no idea why, but when I started to see things in terms of branches, leaves, and flowcharts I had an enlightenment moment and suddenly many of the topics that were a struggled became more tolerable to comprehend. How happy I was!

Photo by Jeremy Bishop on Unsplash

See, right after this realization, I started using decision trees for many of my pet projects; Pokemon data, gaming data, and the inevitable Iris dataset were some of the ones who traversed the twigs and boughs of your leafy brother. Not only that, for my thesis, guess what I used? Exactly.

During one of these tree-climbing expeditions, I decided to become a dendrologist and learn how such an algorithm is structured. So, I looked to answer some of the following questions: What exactly is a node? How is the tree made? Oh, wait, can I also use it for regression? I was purely amazed. Amid this adventure, I discovered you. You random forest, an ensemble of my fond trees. What a good day that was.

Photo by Lukasz Szmigiel on Unsplash

After I got to know you, I went to many, many hikes through your forest. Suddenly, I had updated most of my previous models, to you — end the era of the lonely tree, and welcome to the ages of the multiple ones! And well, I don’t want to brag, but I knew several things about you; I went from a dendrologist to a forester. Want to know something great? Back when I got my first job, I used you for my first supervised learning task! Of course, I did! I remember fitting a spring-ish, vast, but-not-so-deep, forest that looked like a National Park. And wow, how graceful you were. Waves and waves of spam, you controlled (and with high confidence, by the way!), making me (and my bosses) really satisfied.

Unfortunately, after some time, we had to replace you. You just became a bit too heavy and slow to train. I don’t mean to offend you! It’s just that our requirements changed, and so did our strategy… or maybe we were just not ready for your grandeur. Even after you were gone, I kept finding traces of your twigs, leaves, and branches among my own forest of code, and every single time it brought a smile to my face; “aha! Looks who’s here”, I said when I saw parts of your whole in line 37. Gone, but not forgotten.

Me talking about you at Berlin Buzzwords 2017

And similarly to how I stopped using you at work, it seems like most of the world also did. Even though Google Trends’ data says otherwise, I feel like your rustling is not as loud as before. Now, I seldom see use cases ruled by you, nor people speaking about you in conferences; it’s like autumn finally arrived at the woods.

But hey, I also heard the good stories! Lately, your cousin gradient boosted trees or Boostry, as I call it, has been all over the news, and that’s fantastic. I mean, with you as a mentor, what could have gone wrong.

So, yes, my good friend, those were my words. I sincerely hope everything is okay with you. However, to end in a positive note, I’ll say that if there’s something I have learned, is that in this field, spring is always around the corner, so I’m sure I’ll be hearing from you.

Your fan, Juan.

Photo by Johannes Plenio on Unsplash