Frequently Asked Questions

In redcapAPI: Interface to 'REDCap'

library(redcapAPI)
url <- "https://redcap.vanderbilt.edu/api/" # Our institutions REDCap instance

unlockREDCap(c(rcon = "Sandbox"), 
             envir = .GlobalEnv,
             keyring = "API_KEYs", 
             url = url)

ExistingProject <- preserveProject(rcon)

\clearpage

Exporting Records

Which is preferred exportRecordsTyped or exportBulkRecords?

This depends on ones preferred use case. It's important to understand the difference in the two and their relationship.

exportRecordsTyped exports a single data.frame of all the data requested.

exportBulkRecords call exportRecordsTyped to create a data.frame for each form in the project, or just those requested via the forms argument. Additional arguments are all passed to exportRecordsTyped. Thus the documentation on validation and casting is the same for both.

If one is starting a new project, we would recommend using exportBulkRecords as the subsetting and filtering of empty rows is taken care of, and the user is left with doing the required joins to the data. If one has existing code they are converting that used exportRecords, then exportRecordsTyped is the recommendation. This is usually followed by code to subset into forms, filtering and then the same joins between these. Thus new projects can save some code by starting with exportBulkRecords.

What is the warning about zero-coded check fields?

The redcapAPI development team strongly advises against the use of zero-coded check fields in project databases.

A zero-coded check field is a field of the REDCap type checkbox that has a coding definition of 0, [label]. When exported, the field names for these fields is [field_name]___0. As in other checkbox fields, the raw data output returns binary values where 0 represent an unchecked box and 1 represents a checked box. For zero-coded checkboxes, then, a value of 1 indicates that 0 was selected.

This coding rarely presents a problem when casting from raw values (as is done in exportRecordsTyped). However, casting from coded or labeled values can be problematic. In this case, it becomes indeterminate from context if the intent of 0 is 'false' or the coded value '0' ('true') ...

The situations in which casting may fail to produce the desired results are

| Code | Label | Result | |------|-------------------------|-----------------------------------------------| | 0 | anything other than "0" | Likely to fail when casting from coded values | | 0 | 0 | Likely to fail when casting from coded or labeled values |

Examples of problematic coding are

0, Stegosaurus     (likely to fail when casting from coded values)
1, Triceratops
2, Brachiosaurus

and

0, 0               (likely to fail when casting for coded or labeled values)
1, 1
2, 2

When it is necessary to cast a zero-coded check field from coded or labeled values, the castCheckForImport casting function is the best option, as it provides the user full control over what values are to be considered "Checked."

redcapAPI is noisy (creates lots of warnings) about the presence of zero-coded check fields. The potential for loss of data integrity is serious and users need to be aware of that potential. The user may disable these warnings in exportRecordsTyped by setting the argument warn_zero_coded = FALSE.

\clearpage

Casting Records

purgeProject(rcon, purge_all= TRUE)
load("data/CastingVignetteData.Rdata")

importArms(rcon, Arms)
importEvents(rcon, Events)
importMetaData(rcon, MetaData)
importProjectInformation(rcon, data.frame(is_longitudinal = 1))
importRecords(rcon, Records)

How do I stop casting fields to factors?

I used to be able to set factors = FALSE to prevent categorical values from being returned as factors. How do I do that with exportRecordsTyped?

Users may substitute an alternate casting list specification within the call to exportRecordsTyped. redcapAPI provides two lists for this purpose: default_cast_character and default_cast_no_factor. These two lists are identical and may be used interchangeably.

exportRecordsTyped(rcon, 
                   cast = default_cast_character)

exportRecordsTyped(rcon, 
                   cast = default_cast_no_factor)

Aside from not casting factors, all other settings in this list are identical to the default casting.

How do I control the casting of redcap_event_name?

In earlier versions of redcapAPI, the redcap_event_name field commonly returned the values such as event_1_arm_1, event_2_arm_1, etc. It now returns "fancy" values. How do I get the original behavior?

The redcap_event_name field is one of the fields referred to as a "system" field. These fields are not part of the project's data dictionary, and are automatically returned by the API based on the configuration of the project.

By default, exportRecordsTyped returns the "labeled" values of the event names.

exportRecordsTyped(rcon, 
                   fields = "redcap_event_name", 
                   records = 1:3)

This behavior can be changed using the system casting override (this will also affect the casting of other system fields).

exportRecordsTyped(rcon, 
                   fields = "redcap_event_name", 
                   records = 1:3, 
                   cast = list(system = castRaw))

Concerns Over Invalid Data Being Marked NA

Users have expressed concern that marking data that fails validation is not desired, as NA(not in REDCap) is not the same as NA(Unable to Cast). While this is true, there is no means to easily differentiate the two in the same data.frame. The problem can be demonstrated with a simple example as follows.

Say that one needs to write a general function that given a vector of strings in R and turn this into a Date object; in type theory this is $f : \texttt{Text} \rightarrow \texttt{Date}$. What if the string presented is "yyz"? There is no date that can be assigned in R and the core date routines in R will throw an error and halt processing. R is somewhat unique in that all it's core data types exist inside the Maybe monad, i.e. Maybe a = Just a | NA. Thus the true function type is $f : \texttt{Text} \rightarrow \texttt{Maybe Date}$. This allows for NA or "not available" values. R makes no judgement on the cause of the lack of availability. To continue processing the only safe choice is to assign "yyz" to NA, $f(`yyz'') = NA$.This was a big driving reason behind the design ofexportRecordsTyped`. The "Typed" portion of the name referring to this. Thus the algorithm:

• Assign NA to all values that are NA by definition from the data collection source.
• Assign NA to all values that cannot be cast into their target types and record this in the invalidRecords attribute.
• Perform the final type casting on the values that have not been assigned NA.

Via inversion of control, the user can override any choices the library team has made in exportRecordsTyped via the na, validation or cast arguments. It should be noted that the validation and cast arguments need to remain consistent with one another for each type.

Because NA has 2 meanings, the scanning of the resulting reviewInvalidRecords report is a crucial and important step in ensuring data quality of preparing data for analysis and reporting.

\clearpage

Missing Data Detection

purgeProject(rcon, purge_all= TRUE)
load("data/MissingDataVignetteData.Rdata")

importArms(rcon, Arms)
importEvents(rcon, Events)
importMetaData(rcon, MetaData)
importProjectInformation(rcon, data.frame(is_longitudinal = 1))
importRecords(rcon, Records)

Change the Default Missing Data Detection for All Field Types

How do I change the default missing data detection for all field types?

redcapAPI has an obscure function that will create a list of overrides for every field type. Use the na_values function to create the override list as illustrated below. (Yes, na_values takes a function as an argument)

customMissingDetection <- function(x, ...){
  is.na(x) | x == "" | x %in% c(-98, -99)
}

Rec <- exportRecordsTyped(rcon,
                          fields = c("days_between", 
                                     "days_between_duplicate", 
                                     "dropdown_example", 
                                     "dropdown_example_duplicate"), 
                          na = na_values(customMissingDetection))
Rec

purgeProject(rcon, purge_all = TRUE)
importProjectInformation(rcon, ExistingProject$project_information)
importArms(rcon, ExistingProject$arms)
importEvents(rcon, ExistingProject$events)
importMetaData(rcon, ExistingProject$meta_data)
importMappings(rcon, ExistingProject$mappings)
importRepeatingInstrumentsEvents(rcon, ExistingProject$repeating_instruments)
if (nrow(ExistingProject$records)){
  importRecords(rcon, ExistingProject$records)
}

redcapAPI documentation built on Oct. 17, 2024, 5:07 p.m.