Provides functionality to assert conditions that have to be met so that errors in data used in analysis pipelines can fail quickly. Similar to 'stopifnot()' but more powerful, friendly, and easier for use in pipelines.
The assertr package supplies a suite of functions designed to verify assumptions about data early in an analysis pipeline so that data errors are spotted early and can be addressed quickly.
This package does not need to be used with the magrittr/dplyr piping mechanism but the examples in this README use them for clarity.
You can install the latest version on CRAN like this
install.packages("assertr")
or you can install the bleeding-edge development version like this:
install.packages("devtools") devtools::install_github("ropenscilabs/assertr")
This package offers five assertion functions, assert
, verify
,
insist
, assert_rows
, and insist_rows
, that are designed to be used
shortly after data-loading in an analysis pipeline...
Let’s say, for example, that the R’s built-in car dataset, mtcars
, was not
built-in but rather procured from an external source that was known for making
errors in data entry or coding. Pretend we wanted to find the average
miles per gallon for each number of engine cylinders. We might want to first,
confirm
This could be written (in order) using assertr
like this:
mtcars %>% verify(nrow(.) > 10) %>% verify(mpg > 0) %>% insist(within_n_sds(4), mpg) %>% assert(in_set(0,1), am, vs) %>% assert_rows(num_row_NAs, within_bounds(0,2), everything()) %>% insist_rows(maha_dist, within_n_mads(10), everything()) %>% group_by(cyl) %>% summarise(avg.mpg=mean(mpg))
If any of these assertions were violated, an error would have been raised and the pipeline would have been terminated early.
assertr
give me?verify
- takes a data frame (its first argument is provided by
the %>%
operator above), and a logical (boolean) expression. Then, verify
evaluates that expression using the scope of the provided data frame. If any
of the logical values of the expression's result are FALSE
, verify
will
raise an error that terminates any further processing of the pipeline.
assert
- takes a data frame, a predicate function, and an arbitrary
number of columns to apply the predicate function to. The predicate function
(a function that returns a logical/boolean value) is then applied to every
element of the columns selected, and will raise an error if it finds any
violations. Internally, the assert
function uses dplyr
's
select
function to extract the columns to test the predicate function on.
insist
- takes a data frame, a predicate-generating function, and an
arbitrary number of columns. For each column, the the predicate-generating
function is applied, returning a predicate. The predicate is then applied to
every element of the columns selected, and will raise an error if it finds any
violations. The reason for using a predicate-generating function to return a
predicate to use against each value in each of the selected rows is so
that, for example, bounds can be dynamically generated based on what the data
look like; this the only way to, say, create bounds that check if each datum is
within x z-scores, since the standard deviation isn't known a priori.
Internally, the insist
function uses dplyr
's select
function to extract
the columns to test the predicate function on.
assert_rows
- takes a data frame, a row reduction function, a predicate
function, and an arbitrary number of columns to apply the predicate function
to. The row reduction function is applied to the data frame, and returns a value
for each row. The predicate function is then applied to every element of vector
returned from the row reduction function, and will raise an error if it finds
any violations. This functionality is useful, for example, in conjunction with
the num_row_NAs()
function to ensure that there is below a certain number of
missing values in each row. Internally, the assert_rows
function uses
dplyr
'sselect
function to extract the columns to test the predicate
function on.
insist_rows
- takes a data frame, a row reduction function, a
predicate-generating
function, and an arbitrary number of columns to apply the predicate function
to. The row reduction function is applied to the data frame, and returns a value
for each row. The predicate-generating function is then applied to the vector
returned from the row reduction function and the resultant predicate is
applied to each element of that vector. It will raise an error if it finds any
violations. This functionality is useful, for example, in conjunction with
the maha_dist()
function to ensure that there are no flagrant outliers.
Internally, the assert_rows
function uses dplyr
'sselect
function to
extract the columns to test the predicate function on.
assertr
also offers three (so far) predicate functions designed to be used
with the assert
and assert_rows
functions:
not_na
- that checks if an element is not NAwithin_bounds
- that returns a predicate function that checks if a numeric
value falls within the bounds supplied, andin_set
- that returns a predicate function that checks if an element is
a member of the set supplied.and predicate generators designed to be used with the insist
and insist_rows
functions:
within_n_sds
- used to dynamically create bounds to check vector elements with
based on standard z-scoreswithin_n_mads
- better method for dynamically creating bounds to check vector
elements with based on 'robust' z-scores (using median absolute deviation)and the following row reduction functions designed to be used with assert_rows
and insist_rows
:
num_row_NAs
- counts number of missing values in each rowmaha_dist
- computes the mahalanobis distance of each row (for outlier
detection). It will coerce categorical variables into numerics if it needs to.Finally, each assertion function has a counterpart that using standard evaluation. The counterpart functions are postfixed by "_" (an underscore).
For more info, check out the assertr
vignette
Or read it here
added row reduction functions like mahalanobis distnace
added assert_rows and insist_rows assert verbs
bug fixes
insist
and within_n_sds
functions and updated vignette and documentations