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Notice however, that there are different modes of NA —the literal constant is of mode "logical" , but it is frequently automatically coerced to other types. One effect of this is that x[NA] has the length of x , but x[c(1, NA)] has length 2. That is because the rules for logical indices apply in the former case, but those for integer indices in the latter.

Indexing with [ will also carry out the relevant subsetting of any names attributes.

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Subsetting multi-dimensional structures generally follows the same rules as single-dimensional indexing for each index variable, with the relevant component of dimnames taking the place of names . A couple of special rules apply, though:

Normally, a structure is accessed using the number of indices corresponding to its dimension. It is however also possible to use a single index in which case the dim and dimnames attributes are disregarded and the result is effectively that of c(m)[i] . Notice that m[1] is usually very different from m[1, ] or m[, 1] .

It is possible to use a matrix of integers as an index. In this case, the number of columns of the matrix should match the number of dimensions of the structure, and the result will be a vector with length as the number of rows of the matrix. The following example shows how to extract the elements m[1, 1] and m[2, 2] in one operation.

Indexing matrices may not contain negative indices. NA and zero values are allowed: rows in an index matrix containing a zero are ignored, whereas rows containing an NA produce an NA in the result.

Both in the case of using a single index and in matrix indexing, a names attribute is used if present, as had the structure been one-dimensional.

If an indexing operation causes the result to have one of its extents of length one, as in selecting a single slice of a three-dimensional matrix with (say) m[2, , ] , the corresponding dimension is generally dropped from the result. If a single-dimensional structure results, a vector is obtained. This is occasionally undesirable and can be turned off by adding the ‘ drop = FALSE ’ to the indexing operation. Notice that this is an additional argument to the [ function and doesn’t add to the index count. Hence the correct way of selecting the first row of a matrix as a 1 by n matrix is m[1, , drop = FALSE] . Forgetting to disable the dropping feature is a common cause of failure in general subroutines where an index occasionally, but not usually has length one. This rule still applies to a one-dimensional array, where any subsetting will give a vector result unless ‘ drop = FALSE ’ is used.

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Co-founded couple of startups(IOT, AI based). Here to write about code, technology, design, finance and my life experience.

This article about structuring the backend for REST API’s which can be extend to Graphql.

After working with many backend projects, i realised that structuring the app is equally important as the choice of tech stack and fractal app structure is always my choice.

Fractal pattern convey that similar patterns recur progressively and the same thought process is applied to the structuring of codebase i.e All units repeat themselves.

Now, lets start with the crux,

App Root Structure

The root folder always remain same in any case of API’s structuring.

So, At root level we have -:

1 . app is where our main app code goes and will discus in depth under app structure below.

2 . docs (optional) is for documentation purpose.

3 . lib (optional) is where the complied app code goes which is used for production env.

4 . migrations is where all the table schema. I personally use Womens Valerie Cami Pyjama Sets Boux Avenue Pick A Best Online Newest Cheap Price Visa Payment For Sale Sale Countdown Package Outlet 2018 WN6IwRqkO
and an self made ORM name Buy Cheap View Black La Maille Sperone Tank Top Jacquemus 2018 Online Buy Cheap Best Prices Hot Sale For Sale Outlet Visit New M6yDdk
written on top of it.

5 . node_modules you already know it 😃.

6 . tests is where we write all our unit test.

The structuring of tests folder is like the actions or routes under app folder and will be explained in app structure section.

7 . config and config.sample.js are where all of our configuration related to database, authentication, external api keys etc are stored.

If you are wondering why we have two such files, then config.sample.js goes to your repository so that other developer can know the file shape and can use to form their local config.js file.

Also, we can also have a config.production for production environment.

8. eslintrc is where the lint logic goes. Read more .

9. migrate is the file that pass our configuration from config.js to ORM and help us run migration from CLI, check the code .

10. gitignore is where we path to folder or filename that we don’t want to push on repository.

11. package.json  — you already know it 😃.

The app Structure

1. server.js is the file that start your server and will have all middleware that is required for request parsing like etc and finally we add routes middleware.

2. routes will have sub-files or sub-folders made as per the entities in project.

The index.js under routes looks like as shown below. It have request handler middlewares and a catch all route.

A file under routes is where all request handler or sub-routes are written and the only purpose of them is to either call the action that is responsible for that route or the sub-route folder.

3. Most of the times actions folder will have same the same structuring as the routes folder.

Each file in actions is forbusiness logic i.e all code that store, get, change real entities either in database tables or doing queuing function like enqueue and dequeue etc all happen here.

4. So, middlewares, utils, helpers, tasks will follow the same way ofstructuring as action or routes do i.e main entity will act as a root folder and then will can have subfolder as per sub-entities and repeat.

5. tasks.js is used for running tasks from CLI created under task folder like database seed, clean database etc.

6. nsqd (optional) is use case specific for distributed messaging.

utils and helpers can be merged if need, i love to keep them separate so that i can reuse utils as its more generic in all projects

Why fractal

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