# Track a Subset of Inputs to Improve Performance

This guide will help users to track only a subset of inputs that are important to the analysis.

One of the main motivations to use this feature in `{shiny.telemetry}` is to reduce the amount of data that is being tracked as some Shiny widgets can generate a lot of events. In particular, on events that are sending input changes triggered via Javascript.

Some widgets will track events, such as mouse clicking on elements or even the position of the cursor, which will have a impact on the application performance and on the amount of data that is being stored.

The developer of the shiny application can achieve this on `{shiny.telemtry}` with 2 complementary strategies:

1. Exclude inputs via a regular expression via the `telemetry$log_all_inputs()` method;

- This is most common use case and is available since version `0.3.0`;

1. Track only specific input ids via the `telemetry$log_input()` method.

To achieve either of these strategies, the user will need disable the tracking of inputs on the `telemetry$start_session` method and then call the appropriate method. note: When calling `telemetry$log_all_inputs()` with the default arguments it will behave just like the `telemetry$start_session` method.

    server <- function(id) {
      moduleServer(id, function(input, output, session) {
        telemetry$start_session(track_inputs = FALSE)

        telemetry$log_input(c("app-input_id_1", "app-input_id_2", "app-ns2-input_id_4")) # 1.
        telemetry$log_all_inputs(excluded_inputs_regex = ".*-namespace2-.*") # 2.

        # Server logic ...
      })
    }

### Exclude inputs via a regular expression

In most applications where `{shiny.telemetry}` is being used, the developers want to track all input changes while excluding a specific subset of input ids or patterns.

To achieve this, the user can call on `telemetry$log_all_inputs()` with the `excluded_inputs_regex` argument.

Let’s say we want to exclude all input ids that are triggered by the `{DT}` package, then we can use the pattern that it should start with `dt_` and contain only alpha numeric characters or underscore. The chunk below shows how to achieve this:

    server <- function(id) {
      moduleServer(id, function(input, output, session) {
        telemetry$start_session(track_inputs = FALSE)
        telemetry$log_all_inputs(excluded_inputs_regex = "dt_[a-zA-Z0-9_]*$"])
        # Server logic ...
      })
    }

In the event of a specific input id that should be included, regardless of the excluded regular expression, the user can call on `telemetry$log_all_inputs()` with the `include_input_ids` argument that will have a higher priority and included in the tracking.

#### Exclude inputs by full input id

Additionally, the user can exclude inputs by the full input id by passing a vector of input ids to the `excluded_inputs` argument.

    server <- function(id) {
      moduleServer(id, function(input, output, session) {
        telemetry$start_session(track_inputs = FALSE)
        telemetry$log_all_inputs(excluded_inputs = c("input_1", "ns2-input_1", "input_2"])
        # Server logic ...
      })
    }

### Track a small subset of input ids

If there is a small subset of inputs that should be tracked while ignoring all others, the the user can call on `telemetry$log_input()` with one or more input ids.

When this function is called, it will create an observe event for each of the input ids that are being tracked.

    server <- function(id) {
      moduleServer(id, function(input, output, session) {
        telemetry$start_session(track_inputs = FALSE)
        telemetry$log_input(c("app-input_id_1", "app-input_id_2", "app-ns2-input_id_4")) # 1.
        # Server logic ...
      })
    }