Interactive documents: An incredibly easy way to use Shiny

Awesome new features!

RStudio Blog

R Markdown’s new interactive documents provide a quick, light-weight way to use Shiny. An interactive document embeds Shiny elements in an R Markdown report. The report becomes “live”, a choose your own adventure that readers can control and explore. Interactive documents are easy to create and easy to share.

Create an interactive document

To create an interactive document use RStudio to create a new R Markdown file, choose the Shiny document template, then click “Run Document” to show a preview:


storms.002

Embed R code chunks in your report where you like. Interactive documents use the same syntax as R Markdown and knitr. Set echo = FALSE. Your reader won’t see the code, just its results.

  storms2.001

Include Shiny widgets and outputs in your code chunks. R Markdown will insert the widgets directly into your final document. When a reader toggles a widget, the parts of the document that depend on it will…

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Interactive documents: An incredibly easy way to use Shiny

Next Permutation

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.
1,2,3 → 1,3,2
3,2,1 → 1,2,3
1,1,5 → 1,5,1

(Java Code on Github at the bottom of the post. )

My thoughts and solution:

Q: What’s the unknown?

A: The next permutation of the current sequence.

Q: What’re the data?

A: An integer array representing a number.

Q: Any Constraints?

A: No extra memory allocation allowed. But I think it means extra memory proportional to the input size N. Besides, at the beginning of solving this problem, we can ignore this constraint.

Q: True. Now what’s the meaning of next permutation?

A: Hmm, I think it means the next number sequence of the current sequence in lexicographic order, e.g., (1,2, 5, 3,4) -> (1,2, 5, 4,3), (1, 5, 3,4,2) -> (1, 5, 4,2,3) and (5, 4,3,2,1) -> (1,2,3,4,5).

Q: Now as a human being, how do you do this?

A: Eh..just think of the smallest number comprised of these digits that is greater than the current sequence. If there is none, we go back to the smallest possible number in all permutation.

Q: OK, but a computer can’t just “think of” the next number. Now how would a computer do that?

A: Hmm, I think we probably need to start with the least digit on the right side. But what next?

Q: Look at the example you listed above. What did you do with each example?

A: In (1,2, 5, 3,4) -> (1,2, 5, 4,3), I start with 4 and look at its left digit, 3. Since 3 < 4, I switch them. Hmm this works for all cases where the second digit is less than the first one. In (1, 5, 3,4,2) -> (1, 5, 4,2,3), I can’t switch 4 and 2 since (1,5,3,2,4) precedes (1,5,3,4,2). Well 3 < 4, I could switch them to get (1,5,4,3,2) but that’s not the correct answer. Hmm…

Q: So how do you get from (1,5,4,3,2) to (1,5,4,2,3)?

A: I could just switch 3 and 2.

Q: OK, what about (1,5,3,4,2,0) to (1,5,4,0,2,3)?

A: Hmm if I switch 3 and 4, I get (1,5,4,3,2,0). To get (1,5,4,0,2,3), I need to reverse 3,2,0 to 0,2,3. OK, I guess we should do like this: scan from the right, find the first digit at index Ind that is less than its previous digit, switch them and reverse the sequence to the right side of Ind.

Q: Well, almost there, but not yet. What about (1,6,3,5,4,0)? According to your algorithm above, the next permutation becomes (1,6,5,0,4,3) while it should be (1,6,4,0,3,5). See the problem?

A: Hmm, so 3 should be the switch point. I got that right, but it should switch with 4 instead of 5. Ah, so 3 should switch its ceiling in the sequence on its right side! We need to go back to find it and swap. Then do the reverse operation.

Q: Correct, what about the time complexity?

A: We scan the sequence and once find the switch point, we go back and find its ceiling, then switch and reverse. End of story. So it’s actually O(n), an linear time algorithm.

Code on github:

 

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Next Permutation

Sending data from client to server and back using shiny

"R" you ready?

post-logo After some time of using shiny I got to the point where I needed to send some arbitrary data from the client to the server, process it with R and return some other data to the client. As a client/server programming newbie this was a challenge for me as I did not want to dive too deep into the world of web programming. I wanted to get the job done using shiny and preferably as little JS/PHP etc. scripting as possible.

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Sending data from client to server and back using shiny

A brief introduction to “apply” in R

What You're Doing Is Rather Desperate

At any R Q&A site, you’ll frequently see an exchange like this one:

Q: How can I use a loop to […insert task here…] ?
A: Don’t. Use one of the apply functions.

So, what are these wondrous apply functions and how do they work? I think the best way to figure out anything in R is to learn by experimentation, using embarrassingly trivial data and functions.

If you fire up your R console, type “??apply” and scroll down to the functions in the base package, you’ll see something like this:

Let’s examine each of those.

1. apply
Description: “Returns a vector or array or list of values obtained by applying a function to margins of an array or matrix.”

OK – we know about vectors/arrays and functions, but what are these “margins”? Simple: either the rows (1), the columns (2) or both (1:2). By “both”, we mean “apply the…

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A brief introduction to “apply” in R