Early math

Here is what I was doing at 5:30 this morning:

Imagine a grid that contained a list of an arbitrary number of things, but displayed only 7 at a time. Suppose the total number is 35. If, when rendering the list, you wanted to have it take you to the “page” on which a specific item appears, how do you figure out what pages that is, assuming everything sorts consistently?

After a lot of scribbling on my white board, here’s what I came up with:

1. Find the position of the item in the overall list. Let’s says it’s position 25.

2. If the position mod 7 != 0 then the page is (count / 7) + 1; in this case (25/7)+1 or 4; otherwise, page is just count/7 or 3.

3. To translate the display page in to a “start at” value (where to start looking in the list), you then have to do ((page-1)*7)+1. In my example, this gets you a value of ((4-1)*7)+1 = 22. What that means is that when I show the list, I need to start at item #22 and display the next 7 items in order to make sure I capture the . (Since 25 > 22 and 25 < 29), we get the section of the list we were looking for. This seems incredibly complicated for something so simple. I know that an .NET gridview control does this natively but I could not use one of those for good reasons. Yes, that's right, I was sitting in my office doing modulus arithmetic at 5:30 this morning, while the rest of the world was sleeping.

Published by Jamie Todd Rubin

Jamie Todd Rubin writes fiction and nonfiction for a variety of publications including Analog, Clarkesworld, The Daily Beast, 99U, Daily Science Fiction, Lightspeed, InterGalactic Medicine Show, and several anthologies. He was featured in Lifehacker’s How I Work series. He has been blogging since 2005. By day, he manages software projects and occasionally writes code. He lives in Falls Church, Virginia with his wife and three children. Find him on Twitter at @jamietr.

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