Blog
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Implementing “filter” with “reduce”, in Ruby and Python
We’re nearly at the end of my tour of the “reduce” function in Ruby and Python. Just as I showed in the previous installment how we can implement the “map” function using “reduce”, I want to show how we can implement another functional-programming standard, “filter”, using “reduce” as well. As before, I’ll show examples in…
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Implementing “map” with “reduce”, in Ruby and Python
This is another installment in my “reduce” series of posts, aimed at helping programmers understand this function, with examples in both Ruby and Python. So far, we have seen how we can build a number of different types of data structures — integers, strings, arrays, and hashes — using “reduce”. But the really interesting use…
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Creating Ruby hashes with “reduce”
In yesterday’s post, I showed how we can use Python’s “reduce” function to create a dictionary. Ruby, of course, also has dictionaries, but calls them “hashes.” In this posting, I’m going to show how we can create a hash in Ruby when iterating over an enumerable. In so doing, we’ll see how we can use…
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Creating Python dictionaries with “reduce”
In the last few installments (first, second, third, and fourth) of this series, we saw how “reduce” can be used to build up a scalar value (such as a number or string), or even a simple collection, such as a list (in Python) or an array (in Ruby). The jewel in the data-structure crown for…
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Creating collections with “reduce”
In the first few parts of this series (first, second, and third), I introduced the “reduce” function, and showed how it can be used in a number of ways. However, in all of the examples we have seen so far, the output from our invocations of “reduce” were integers or strings. If we reduce with…
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Implementing “min” and “max” with “reduce”
This is the third installment of my “reduce” series of blog posts. For the first, see here, and for the second, see here. If you have been reading this series, then you know that “reduce” can be used to sum numbers, or to calculate scores. In that sense, “reduce” justifies its name; we’re invoking a…
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Calculating Scrabble scores with “reduce”
This is the second installment of my series of blog posts on the “reduce” function/method. For an introduction, see here. I love to play Scrabble — or more commonly nowadays, I play Words with Friends on my phone. (I often say that the game should instead be called, “Words with people who used to be your…
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Understanding “reduce” (first in a series)
One of the notable things about MIT’s computer science curriculum, at least back when I was studying there, was that you didn’t learn any “practical” programming languages. Our work was all done in either Scheme (a dialect of Lisp) or in CLU (an early object-oriented language). I can’t say that I have too many memories,…
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If you build it, they will come — but they might hate you
Several months ago, I was teaching an introductory Python course, and I happened to mention the fact that I use Git for all of my version-control needs. I think that I would have gotten a more positive response if I had told them that my hobby is kicking puppies. The reactions were roughly — and…
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Good intentions, unexpected results: Mailing lists and DMARC
If there’s anything that software people know, it’s that changing one part of a program can result in a change in a seemingly unrelated part of the program. That’s why automated testing is so powerful; it can show you when you have made a mistake that you not only didn’t intend, but that you didn’t…