Pipeline

In the last tutorial, the basic element of PipeScript was introduced. The Transform.

To reiterate in more detail, a Transform can be:

• An algebraic or logical statement: ($ + 5)/2 > 5 or $ < 3
• A transform function call (if($>5) or equivalently if $>5. Both function-call and bash-like syntax are allowed.)
• A mixture of the two

The Pipeline

If you have ever used bash pipes, you will be right at home in PipeScript. PipeScript is made with the same principles in mind. You create a script by piping together the outputs of several transforms, to create what we call a Pipeline.

a | b | c | d

For example, suppose that we have the following data from a fitness tracker:

[
{
    "t": 1,
    "d": {
          "steps": 14,
          "activity": "walking",
        }
},
{
    "t": 2,
    "d": {
          "steps": 10,
          "activity": "running",
        }
},
{
    "t": 3,
    "d": {
          "steps": 12,
          "activity": "walking",
        }
},{
    "t": 4,
    "d": {
          "steps": 5,
          "activity": "running",
        }
},]

We want to get the total number of steps we took while running. We cannot do this with one transform, but by chaining together a couple simple transforms, we can get there!

First off, we want to pass through only the datapoints where we were running:

if $("activity") == "running"

Notice that the identity operator $ accepts an argument - it allows you to return a sub-object of your Datapoint. Our result is:

[
{
    "t": 2,
    "d": {
          "steps": 10,
          "activity": "running",
        }
},
{
    "t": 4,
    "d": {
          "steps": 5,
          "activity": "running",
        }
},]

Now, let's extract the number of steps from the json object:

if $("activity") == "running" | $("steps")

[{
    "t": 2,
    "d": 10
},{
    "t": 4,
    "d": 5
},]

Next, we want to get their sum:

if $("activity") == "running" | $("steps") | sum

[{
    "t": 2,
    "d": 10
},{
    "t": 4,
    "d": 15
},]

This is almost there! Our second datapoint has the answer we were looking for, but the pipeline also returns the intermediate result. Therefore, we add a final transform to the end of the pipeline:

if $("activity") == "running" | $("steps") | sum | if last

[{
    "t": 4,
    "d": 15
},]

And this is the result we were looking for!

In the third tutorial, you will learn about one more cute feature of PipeScript: sub-pipelines.