derive_param_computed: Adds a Parameter Computed from the Analysis Value of Other...

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Adds a Parameter Computed from the Analysis Value of Other Parameters

Description

Adds a parameter computed from the analysis value of other parameters. It is expected that the analysis value of the new parameter is defined by an expression using the analysis values of other parameters, such as addition/sum, subtraction/difference, multiplication/product, division/ratio, exponentiation/logarithm, or by formula.

For example mean arterial pressure (MAP) can be derived from systolic (SYSBP) and diastolic blood pressure (DIABP) with the formula

MAP = \frac{SYSBP + 2 DIABP}{3}

Usage

derive_param_computed(
  dataset = NULL,
  dataset_add = NULL,
  by_vars,
  parameters,
  set_values_to,
  filter = NULL,
  constant_by_vars = NULL,
  constant_parameters = NULL,
  keep_nas = FALSE
)

Arguments

dataset	Input dataset The variables specified by the by_vars argument are expected to be in the dataset. PARAMCD is expected as well. The variable specified by by_vars and PARAMCD must be a unique key of the input dataset after restricting it by the filter condition (filter parameter) and to the parameters specified by parameters.
dataset_add	Additional dataset The variables specified by the by_vars parameter are expected. The variable specified by by_vars and PARAMCD must be a unique key of the additional dataset after restricting it to the parameters specified by parameters. If the argument is specified, the observations of the additional dataset are considered in addition to the observations from the input dataset (dataset restricted by filter).
by_vars	Grouping variables For each group defined by by_vars an observation is added to the output dataset. Only variables specified in by_vars will be populated in the newly created records.
parameters	Required parameter codes It is expected that all parameter codes (PARAMCD) which are required to derive the new parameter are specified for this parameter or the constant_parameters parameter. If observations should be considered which do not have a parameter code, e.g., if an SDTM dataset is used, temporary parameter codes can be derived by specifying a list of expressions. The name of the element defines the temporary parameter code and the expression the condition for selecting the records. For example parameters = exprs(HGHT = VSTESTCD == "HEIGHT") selects the observations with VSTESTCD == "HEIGHT" from the input data (dataset and dataset_add), sets PARAMCD = "HGHT" for these observations, and adds them to the observations to consider. Unnamed elements in the list of expressions are considered as parameter codes. For example, parameters = exprs(WEIGHT, HGHT = VSTESTCD == "HEIGHT") uses the parameter code "WEIGHT" and creates a temporary parameter code "HGHT".
set_values_to	Variables to be set The specified variables are set to the specified values for the new observations. The values of variables of the parameters specified by parameters can be accessed using ⁠<variable name>.<parameter code>⁠. For example exprs( AVAL = (AVAL.SYSBP + 2 * AVAL.DIABP) / 3, PARAMCD = "MAP" ) defines the analysis value and parameter code for the new parameter. Variable names in the expression must not contain more than one dot. Note that dplyr helper functions such as dplyr::starts_with() should be avoided unless the list of variable-value pairs is clearly specified in a statement via the set_values_to argument.
filter	Filter condition The specified condition is applied to the input dataset before deriving the new parameter, i.e., only observations fulfilling the condition are taken into account.
constant_by_vars	By variables for constant parameters The constant parameters (parameters that are measured only once) are merged to the other parameters using the specified variables. (Refer to Example 2)
constant_parameters	Required constant parameter codes It is expected that all the parameter codes (PARAMCD) which are required to derive the new parameter and are measured only once are specified here. For example if BMI should be derived and height is measured only once while weight is measured at each visit. Height could be specified in the constant_parameters parameter. (Refer to Example 2) If observations should be considered which do not have a parameter code, e.g., if an SDTM dataset is used, temporary parameter codes can be derived by specifying a list of expressions. The name of the element defines the temporary parameter code and the expression the condition for selecting the records. For example constant_parameters = exprs(HGHT = VSTESTCD == "HEIGHT") selects the observations with VSTESTCD == "HEIGHT" from the input data (dataset and dataset_add), sets PARAMCD = "HGHT" for these observations, and adds them to the observations to consider. Unnamed elements in the list of expressions are considered as parameter codes. For example, constant_parameters = exprs(WEIGHT, HGHT = VSTESTCD == "HEIGHT") uses the parameter code "WEIGHT" and creates a temporary parameter code "HGHT".
keep_nas	Keep observations with NAs If the argument is set to TRUE, observations are added even if some of the values contributing to the computed value are NA (see Example 1b). If the argument is set to a list of variables, observations are added even if some of specified variables are NA (see Example 1c).

Details

For each group (with respect to the variables specified for the by_vars parameter) an observation is added to the output dataset if the filtered input dataset (dataset) or the additional dataset (dataset_add) contains exactly one observation for each parameter code specified for parameters and all contributing values like AVAL.SYSBP are not NA. The keep_nas can be used to specify variables for which NAs are acceptable. See also Example 1b and 1c.

For the new observations the variables specified for set_values_to are set to the provided values. The values of the other variables of the input dataset are set to NA.

Value

The input dataset with the new parameter added. Note, a variable will only be populated in the new parameter rows if it is specified in by_vars.

See Also

BDS-Findings Functions for adding Parameters/Records: default_qtc_paramcd(), derive_expected_records(), derive_extreme_event(), derive_extreme_records(), derive_locf_records(), derive_param_bmi(), derive_param_bsa(), derive_param_doseint(), derive_param_exist_flag(), derive_param_exposure(), derive_param_framingham(), derive_param_map(), derive_param_qtc(), derive_param_rr(), derive_param_wbc_abs(), derive_summary_records()

admiral documentation built on May 28, 2026, 9:08 a.m.