Functional way of re-using variables in a pipe

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Using functional programming in javascript and typescript together with Ramda, I often find myself writing code like:

const myFun = c => {
  const myId = c.id

  const value = pipe(
    getAnotherOtherPropOfC,
    transformToArray,
    mapToSomething,
    filterSomething,
    // ... N other transformations
    // ok now I need myId and also the result of the previous function
    chainMyIdWithResultOfPreviousFunction(myId)
  )(c)

  return value
}

Notice how creating a const myId breaks point-free style. I'd like to write myFun so that there's no need to explicit c. So something like: const myFun = pipe(....)

I was wondering if there's a more functional and readable way of doing things like this.

Can it be done? Sure. Should it be done? It's not so clear.

Here is a point-free version of the above, using lift:

const getAnotherOtherPropOfC = prop ('x')
const transformToArray = split (/,\s*/)
const mapToSomething = map (Number)
const filterSomething = filter (n => n % 2 == 1)
const square = (n) => n * n
const chainMyIdWithResultOfPreviousFunction = (id) => (arr) => `${id}: [${arr}]`

const myFun = lift (chainMyIdWithResultOfPreviousFunction) (
  prop ('id'),
  pipe(
    getAnotherOtherPropOfC,
    transformToArray,
    mapToSomething,
    filterSomething,
    map (square)
  )
)

console .log (
  myFun ({id: 'foo', x: '1, 2, 3, 4, 5'}) // => 'foo: [1,9,25]'
)
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>
<script> const {prop, split, map, filter, lift, pipe} = R            </script>

Reusing intermediate values in F# pipe, Sometimes, I'd like to use intermediate values arising when pipeline is Now, we can see that inputList variable is only visible inside lambda function. I hope you will find something useful here, but just use a way that you  Consider, for example, the lm () function or the with () function. These functions are useful in a pipeline where your data is first processed and then passed into the function. For functions that don't have a data argument, such as the cor () function, it's still handy if you can expose the variables in the data.

Variables are usually an indication that your function is doing too much and should be decomposed. For example, this

const myFun = c => {
    let id = c.id;

    return R.pipe(
        R.prop('list'),
        R.map(R.add(10)),
        R.sum,
        R.subtract(id),
    )(c)
}

can be refactored into two separate functions:

const compute = R.pipe(
    R.prop('list'),
    R.map(R.add(10)),
    R.sum,
);

const getId = R.prop('id');

and then simply

const myFun = c => getId(c) - compute(c)

which looks good enough to me, but if you want to be absolutely point-free, then

const myFun = R.converge(R.subtract, [getId, compute])

Playground

18 Pipes, 20.4.1 Coercion · 20.4.2 Test functions · 20.4.3 Scalars and recycling rules The point of the pipe is to help you write code in a way that is easier to read and understand. And we'll use a function for each key verb: hop() , scoop() , and bop() . That means the carat variable can no longer be shared between the two data  If we use pipe operator, the_data <- read.csv ("/path/to/data/file.csv") %>% subset (variable_a > x) %>% transform (variable_c = variable_a / variable_b) %>% head (100) Hint: In RStudio, you could use Ctrl + Shift + M (or Cmd + Shift + M) to insert the pipe operator.

Please note that I use vanilla JS to reach a wider audiance.

A pipe is just a composite function is just a function. So let's use a higher order pipe that takes a pipe, a function and a value and returns another function instead of the result. To actually get the result we need to pass the value twice:

const toUc = s => s.toUpperCase();
const double = s => `${s}${s}`;
const shout = s => `${s}!`;
const concat = t => s => `${s} -> ${t}`;

const pipe = g => f => x => f(g(x));
const pipe3 = h => g => f => x => f(g(h(x)));

const foo = {id: "hi"};
const bar = pipe3(toUc) (shout) (double); // pipe

const baz = pipe(bar) (concat); // higher order pipe

// the result of the applied pipe is just another function because concat requires two arguments!

console.log(
  baz(foo.id)) // s => `${s} -> ${t}`

// let's apply it twice

console.log(
  baz(foo.id)
    (foo.id)); // hi -> HI!HI!

Thinking in Ramda: Combining Functions, This post is Part 2 of a series about functional programming called Even better is to give the complement ed function its own name so it can be reused: written our original operate function is to inline all of the temporary variables: compose works exactly the same way as pipe , except that it applies the  To prevent the > and < characters from causing redirection, escape with a caret: ^> or ^< Redirect multiple lines by bracketing a set of commands: ( Echo sample text1 Echo sample text2 ) > c:\logfile.txt Exit Codes. If the filename or command is not found then redirection will set an Exit Code of 1. Unicode

What about something like this:

const getAnotherPropOfC = R.prop('message');
const transformToArray = R.split('');
const mapToSomething = R.map(R.toUpper);
const filterSomething = R.reject(R.equals(' '));
const chainMyIdWithResultOfPreviousFunction = R.pipe(
  R.prop('fragment'), 
  R.concat,
);

const myFun = R.converge(R.map, [
  chainMyIdWithResultOfPreviousFunction,
  R.pipe(
    getAnotherPropOfC,
    transformToArray,
    mapToSomething,
    filterSomething,
  ),
]);



console.log(
  myFun({ message: 'Hello World', fragment: '!' }),
);
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>

Maintenance and Reuse Best Practices for Jenkins Plugins, your Jenkins pipelines continue to grow there are built-in methods for Imagine a large organization with many teams and Jenkins pipeline jobs. They are installed by the Global Variable String Parameter Plugin. If many pipeline scripts reuse the same script function, put that script in a shared library. None of the repeating variables can be dimensionless No two repeating variables can have the same overall dimension. For instance, D, the pipe diameter, and r, the roughness height, both have dimension of L, and so cannot both be used as repeating variables. Select one other variable - say D.

Function Composition in JavaScript with Pipe, You could avoid the intermediate variables by nesting the function calls. The pipe utility is possible in JavaScript because JavaScript functions are first The easiest way to handle a variable list of values is with an array. In order to get better left-to-right readability, we can use a pipe function. This is a common functional pattern that can be done with a simple function: function pipe (fns) { return (arg) => fns.reduce ( (prev, fn) => fn (prev), arg); } What this does is return a new higher-order function that takes a single argument.

JavaScript best practices, None of these make much sense — good variable and function names should be The easiest way to check the syntactical quality of your code is to run it through The shortcut notation for this is the double pipe character: to create a more generic helper function instead, and reuse that functionality where it is needed. variable=$(complex_command) as in. message=$(echo 'hello') (or for that matter, message=hello in this case). Your pipeline: echo 'hello' | message=$(</dev/stdin) or. echo 'hello' | read message actually works. The only problem is that the shell that you're using will run the second part of the pipeline in a subshell.

The tidy tools manifesto • tidyverse, Reuse existing data structures. Compose simple functions with the pipe. Embrace functional programming. Design for Assume the data is tidy, with variables in the columns, and observations in the rows (see Tidy Data for more details). in isolation, and have a standard way to combine with other pieces. The pipe operator passes the preceding object as an argument to the object that follows the pipe, so x %>% f can be transformed into f(x). Consequently, the pipe operator can be defined using Infix as follows:

Comments
  • Using a variable multiple time is much easier and readable without pointfree style.
  • Is there anything wrong with a second input? I.e. const myFun = (c, id) => {...}
  • I like this approach. I didn't know about the converge function so thanks! I'm still wondering if this pattern covers the majority of the cases in which I need to reuse variables in a pipe. What if R.subtract(id) and R.sum are switched in the original myFun? (meaning that id is not used in the last function of the pipe, but in the middle of it, and potentially reused N times more inside the pipe)