redcap_read: Read records from a REDCap project in subsets, and stacks them together before returning a data.frame.


From an external perspective, this function is similar to redcap_read_oneshot. The internals differ in that redcap_read retrieves subsets of the data, and then combines them before returning (among other objects) a single data.frame. This function can be more appropriate than redcap_read_oneshot when returning large datasets that could tie up the server.


redcap_read(batch_size = 100L, interbatch_delay = 0.5,
  continue_on_error = FALSE, redcap_uri, token, records = NULL,
  records_collapsed = "", fields = NULL, fields_collapsed = "",
  events = NULL, events_collapsed = "", export_data_access_groups = FALSE,
  filter_logic = "", raw_or_label = "raw", verbose = TRUE,
  config_options = NULL, id_position = 1L)



The maximum number of subject records a single batch should contain. The default is 100.


The number of seconds the function will wait before requesting a new subset from REDCap. The default is 0.5 seconds.


If an error occurs while reading, should records in subsequent batches be attempted. The default is FALSE, which prevents subsequent batches from running. Required.


The URI (uniform resource identifier) of the REDCap project. Required.


The user-specific string that serves as the password for a project. Required.


An array, where each element corresponds to the ID of a desired record. Optional.


A single string, where the desired ID values are separated by commas. Optional.


An array, where each element corresponds a desired project field. Optional.


A single string, where the desired field names are separated by commas. Optional.


An array, where each element corresponds a desired project event Optional.


A single string, where the desired event names are separated by commas. Optional.


A boolean value that specifies whether or not to export the “redcap_data_access_group” field when data access groups are utilized in the project. Default is FALSE. See the details below.


String of logic text (e.g., [gender] = 'male') for filtering the data to be returned by this API method, in which the API will only return the records (or record-events, if a longitudinal project) where the logic evaluates as TRUE. An blank/empty string returns all records.


A string (either 'raw' or 'label' that specifies whether to export the raw coded values or the labels for the options of multiple choice fields. Default is 'raw'.


A boolean value indicating if messages should be printed to the R console during the operation. The verbose output might contain sensitive information (e.g. PHI), so turn this off if the output might be visible somewhere public. Optional.


A list of options to pass to POST method in the httr package. See the details in redcap_read_oneshot() Optional.


The column position of the variable that unique identifies the subject. This defaults to the first variable in the dataset.


Specifically, it internally uses multiple calls to redcap_read_oneshot to select and return data. Initially, only primary key is queried through the REDCap API. The long list is then subsetted into partitions, whose sizes are determined by the batch_size parameter. REDCap is then queried for all variables of the subset's subjects. This is repeated for each subset, before returning a unified data.frame.

The function allows a delay between calls, which allows the server to attend to other users' requests.

For redcap_read to function properly, the user must have Export permissions for the ‘Full Data Set’. Users with only ‘De-Identified’ export privileges can still use redcap_read_oneshot. To grant the appropriate permissions:

  1. go to ‘User Rights’ in the REDCap project site,

  2. select the desired user, and then select ‘Edit User Privileges’,

  3. in the ‘Data Exports’ radio buttons, select ‘Full Data Set’.


Currently, a list is returned with the following elements,

  1. data: An R data.frame of the desired records and columns.

  2. success: A boolean value indicating if the operation was apparently successful.

  3. status_codes: A collection of http status codes, separated by semicolons. There is one code for each batch attempted.

  4. outcome_messages: A collection of human readable strings indicating the operations' semicolons. There is one code for each batch attempted. In an unsuccessful operation, it should contain diagnostic information.

  5. records_collapsed: The desired records IDs, collapsed into a single string, separated by commas.

  6. fields_collapsed: The desired field names, collapsed into a single string, separated by commas.

  7. filter_logic: The filter statement passed as an argument.

  8. elapsed_seconds: The duration of the function.


Will Beasley


The official documentation can be found on the ‘API Help Page' and 'API Examples’ pages on the REDCap wiki (ie, and If you do not have an account for the wiki, please ask your campus REDCap administrator to send you the static material.

The official cURL site discusses the process of using SSL to verify the server being connected to.


## Not run: 
library(REDCapR) #Load the package into the current R session.
uri     <- ""
token   <- "9A81268476645C4E5F03428B8AC3AA7B"
redcap_read(batch_size=2, redcap_uri=uri, token=token)

## End(Not run)

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