Tracking specific events

Tracking methods supported by the Lua Tracker at a glance:

Function	Description
trackScreenView()	Track the user viewing a screen within the application
trackStructEvent()	Track a Snowplow custom structured event
trackUnstructEvent()	Track a Snowplow custom unstructured event

Common

All events are tracked with specific methods on the tracker instance, of the form track...(), where XXX is the name of the event to track.

Argument validation

Lua is a dynamically typed language, but each of our track...() methods expects its arguments to be of specific types and value ranges, and validates that to be the case.

If the validation check fails, then a runtime error is thrown:

local t = snowplow.newTrackerForCf( "d3rkrsqld9gmqf" )
local f = function() t:setColorDepth( "unknown" ) end
assert.has_error( f, "depth is required and must be a positive integer, not [unknown]" ) # Busted assertion passes

If your value is of the wrong type, convert it before passing it into the track...() method, for example:

local level_idx = 42
t:trackScreenView( "Game Level", tostring( level_idx ) )

We specify the types and value ranges required for each argument below.

Optional timestamp argument

Each track...() method supports an optional timestamp as its final argument; this allows you to manually override the timestamp attached to this event.

If you do not pass this timestamp in as an argument, then the Lua Tracker will use the current time to be the timestamp for the event.

Here is an example tracking a structured event and supplying the optional timestamp argument. Note that we have to explicitly supply nils for the intervening arguments which are empty:

t:trackStructEvent( "hud", "save", nil, nil, nil, 1368725287 )

Timestamp is counted in seconds since the Unix epoch – the same format as generated by os.time() in Lua.

Return values

Each track...() method has the same return signature, returning two values:

local status, msg = t:trackUnstructEvent( "save-game", { save_id = "4321", level = 23 } )

These values are as follows:

1. The first value (status above) is a boolean, set to true if the event was successfully logged to the collector, or false if the event was not successfully logged
2. The second value (msg above) is a string, which is nil if status is true, but contains the error message if status be false

Track screen views with trackScreenView()

Use trackScreenView() to track a user viewing a screen (or equivalent) within your app. Arguments are:

Argument	Description	Required?	Validation
name	Human-readable name for this screen	Yes	Non-empty string
id	Unique identifier for this screen	No	String or nil
tstamp	When the screen was viewed	No	Positive integer or nil

Example:

local s, msg = t:trackScreenView( "HUD > Save Game", "screen23", 1368725287 )

Track structured events with trackStructEvent()

Use trackStructEvent() to track a custom event happening in your app which fits the Google Analytics-style structure of having up to five fields (with only the first two required):

Argument	Description	Required?	Validation
category	The grouping of structured events which this action belongs to	Yes	Non-empty string
action	Defines the type of user interaction which this event involves	Yes	Non-empty string
label	A string to provide additional dimensions to the event data	No	String or nil
property	A string describing the object or the action performed on it	No	String or nil
value	A value to provide numerical data about the event	No	Number of nil
tstamp	When the structured event occurred	No	Positive integer or nil

Example:

local s, msg = t:trackStructEvent( "shop", "add-to-basket", nil, "pcs", 2, 1369330909 )

Track unstructured events with trackUnstructEvent()

Use trackUnstructEvent() to track a custom event which consists of a name and an unstructured set of properties. This is useful when:

• You want to track event types which are proprietary/specific to your business (i.e. not already part of Snowplow), or
• You want to track events which have unpredictable or frequently changing properties

The arguments are as follows:

Argument	Description	Required?	Validation
name	The name of the event	Yes	Non-empty string
properties	The properties of the event	Yes	Non-empty table
tstamp	When the screen was viewed	No	Positive integer or nil

Example:

local s, msg = t:trackUnstructEvent( "save-game", {
                   save_id = "4321",
                   level = 23,
                   difficultyLevel = "HARD",
                   dl_content = true
                 }, 1369330929 )

The properties table consists of a set of individual name = value pairs. The structure must be flat: properties cannot be nested. Be careful here as this is not currently enforced through validation.

Supported datatypes

Snowplow unstructured events support a relatively rich set of datatypes. Because these datatypes do not always map directly onto Lua datatypes, we have introduced some “type suffixes” for the Lua property names, so that Snowplow knows what Snowplow data types the Lua data types map onto:

Snowplow datatype	Description	Lua datatype	Type suffix(es)	Supports array?
Null	Absence of a value	N/A	–	No
String	String of characters	string	–	Yes
Boolean	True or false	boolean	–	Yes
Integer	Number without decimal	number	_INT	Yes
Floating point	Number with decimal	number	_FLT	Yes
Geo-coordinates	Longitude and latitude	{ number, number }	_GEO	Yes
Date	Date and time (ms precision)	number	_DT, _TM, _TMS	Yes
Array	Array of values	{x, y, z}	–	–

Let”s go through each of these in turn, providing some examples as we go:

Null

Tracking a Null value for a given field is currently unsupported in the Lua Tracker. There is a ticket to fix this.

String

Tracking a String is easy:

{
    product_id = "ASO01043"
}

Boolean

Tracking a Boolean is also straightforward:

{
    trial = true
}

Integer

To track an Integer, use a Lua number but add a type suffix like so:

{
    in_stock_INT = 23
}

Warning: if you do not add the _INT type suffix, Snowplow will assume you are tracking a Floating point number.

Floating point

To track a Floating point number, use a Lua number; adding a type suffix is optional:

{
    price_INT = 4.99,
    sales_tax = 49.99 -- Same as sales_tax_FLT = ...
}

Geo-coordinates

Tracking a pair of Geographic coordinates is done like so:

{
    check_in_GEO = { 40.11041, -88.21337 } -- Lat, long
}

Please note that the datatype takes the format latitude followed by longitude. That is the same order used by services such as Google Maps.

Warning: if you do not add the _GEO type suffix, then the value will be incorrectly interpreted by Snowplow as an Array of Floating points.

Date

Snowplow Dates include the date and the time, with milliseconds precision. There are three type suffixes supported for tracking a Date:

• _DT – the Number of days since the epoch
• _TM – the Number of seconds since the epoch
• _TMS – the Number of milliseconds since the epoch. This precision is hard to access from within Lua

You can track a date by adding a Lua number to your properties object. The following are all valid dates:

{
    birthday2_DT = 3996,
    registered2_TM = 1371129610,
    last_action_TMS = 1368454114215, -- Accurate to milliseconds
}

Note that the type prefix only indicates how the Lua number sent to Snowplow is interpreted – all Snowplow Dates are stored to milliseconds precision (whether or not they include that level of precision).

Two warnings:

1. If you specify a Lua number but do not add a valid Date suffix (_DT, _TM or _TMS), then the value will be incorrectly interpreted by Snowplow as a Number, not a Date
2. If you specify a Lua number but add the wrong Date suffix, then the Date will be incorrectly interpreted by Snowplow, for example:

{
    last_ping_DT = 1371129610 -- Should have been _TM. Snowplow will interpret this as the year 3756521449
}

Arrays

You can track an Array of values of any data type other than Null.

Arrays must be homogeneous – in other words, all values within the Array must be of the same datatype. This means that the following is not allowed:

{
    sizes = { "xs", 28, "l", 38, "xxl"] -- NOT allowed
}

By contrast, the following are all allowed:

{
    sizes = { "xs", "s", "l", "xl", "xxl" },
    session_starts_TM = { 1371129610, 1064329730, 1341127611 },
    check_ins_GEO = { { -88.21337, 40.11041 }, { -78.81557, 30.22047 } }
}