Package 'zmisc'

Lookup values from a lookup table

Description

The lookup() function implements lookup of values (such as variable names) from a lookup table which maps keys onto values (such as variable labels or descriptions).

The lookup table can be in the form of a two-column data.frame, in the form of a named vector, or in the form of a list. If the table is in the form of a data.frame, the key column should be named either key or name, and the value column should be named value (for the value). If the lookup table is in the form of a named vector or list, the names are used as the key, and the returned value is taken from the values in the vector or list.

The underlying lookup is done using base::match(), and all atomic data types except factor are supported. Factors are omitted due to the ambiguity in what should be looked up (the values or the levels). It is important that x, .default and the columns of lookup_table are all of the same type (specifically of the same base::mode()). If the lookup table is specified as a vector or list, only the character variables are supported, because name(lookup_table) is always of mode character.

Original values are returned if they are not found in the lookup table. Alternatively, a .default can be specified for values that are not found. Note that it is possible to specify NA as one of the keys to look up NA values (only when using a data.frame as lookup table).

Any names or attributes of x are preserved.

The lookuper() function returns a function equivalent to the lookup() function, except that instead of taking a lookup table as an argument, the lookup table is embedded in the function itself.

This can be very useful, in particular when using the lookup function as an argument to other functions that expect a function which maps character->character (or other data types), but do not offer a good way to pass additional arguments to that function.

Usage

lookup(x, lookup_table, ..., .default = x)

lookuper(lookup_table, ..., .default = NULL)

Arguments

x	A vector whose elements are to be looked up.
lookup_table	The lookup table to use.
...	Reserved for future use.
.default	If a value is not found in the lookup table, the value will be taken from .default. This must be a vector of the same mode as x, and either of length 1 or the same length as x. Useful values include x (the default setting), NA, or "" (an empty string). Specifying .default = NULL implies that x will be used for missing values.

Value

The lookup() function returns a vector based on x, with values replaced with the lookup values from lookup_table. Any values not found in the lookup table are taken from .default.

The lookuper() function returns a function that takes vectors as its argument x, and returns either the corresponding values from the underlying lookup table, or the original values from x for those elements that are not found in the lookup table (or looks them up from the default).

Examples

fruit_lookup_vector <- c(a = "Apple", b = "Banana", c = "Cherry")
lookup(letters[1:5], fruit_lookup_vector)
lookup(letters[1:5], fruit_lookup_vector, .default = NA)

mtcars_lookup_data_frame <- data.frame(
  name = c("mpg", "hp", "wt"),
  value = c("Miles/(US) gallon", "Gross horsepower", "Weight (1000 lbs)"))
lookup(names(mtcars), mtcars_lookup_data_frame)

# A more complex example, with numeric and NA values
numeric_lookup_table <- data.frame(
  key = c(1:5, NA), value = c(sqrt(1:5), 99999))
lookup(c(0:6, NA), numeric_lookup_table)

lookup_fruits <- lookuper(list(a = "Apple", b = "Banana", c = "Cherry"))
lookup_fruits(letters[1:5])
lookup_fruits_nomatch_na <-
  lookuper(list(a = "Apple", b = "Banana", c = "Cherry"), .default = NA)
lookup_fruits_nomatch_na(letters[1:5])

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Embed factor levels and value labels in values.

Description

This function adds level/label information as an annotation to either factors or labelled variables. This function is called notate() rather than annotate() to avoid conflict with ggplot2::annotate(). It is a generic that can operate either on individual vectors or on a data.frame.

When printing labelled variables from a tibble in a console, both the numeric value and the text label are shown, but no variable labels. When using the View() function, only variable labels are shown but no value labels. For factors, there is no way to view the integer levels and values at the same time.

In order to allow the viewing of both variable and value labels at the same time, this function converts both factor and labelled variables to character, including both numeric levels (labelled values) and character values (labelled labels) in the output.

Usage

notate(x)

Arguments

x	The object (either vector or date.frame of vectors), that one desires to annotate and/or view.

Value

The processed data.frame, suitable for viewing, in particular through the View() function.

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Sample from a vector in a safe way

Description

The zample() function duplicates the functionality of sample(), with the exception that it does not attempt the (sometimes dangerous) user-friendliness of switching the interpretation of the first element to a number if the length of the vector is 1. zample() always treats its first argument as a vector containing elements that should be sampled, so your code won't break in unexpected ways when the input vector happens to be of length 1.

Usage

zample(x, size = length(x), replace = FALSE, prob = NULL)

Arguments

x	The vector to sample from
size	The number of elements to sample from x (defaults to length(x))
replace	Should elements be replaced after sampling (defaults to false)
prob	A vector of probability weights (defaults to equal probabilities)

Details

If what you really want is to sample from an interval between 1 and n, you can use sample(n) or sample.int(n) (but make sure to only pass vectors of length one to those functions).

Value

The resulting sample

Examples

# For vectors of length 2 or more, zample() and sample() are identical
set.seed(42); zample(7:11)
set.seed(42); sample(7:11)

# For vectors of length 1, zample() will still sample from the vector,
# whereas sample() will "magically" switch to interpreting the input
# as a number n, and sampling from the vector 1:n.
set.seed(42); zample(7)
set.seed(42); sample(7)

# The other arguments work in the same way as for sample()
set.seed(42); zample(7:11, size=13, replace=TRUE, prob=(5:1)^3)
set.seed(42); sample(7:11, size=13, replace=TRUE, prob=(5:1)^3)

# Of course, sampling more than the available elements without
# setting replace=TRUE will result in an error
set.seed(42); tryCatch(zample(7, size=2), error=wrap_error)

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Generate sequence in a safe way

Description

The zeq() function creates an increasing integer sequence, but differs from the standard one in that it will not silently generate a decreasing sequence when the second argument is smaller than the first. If the second argument is one smaller than the first it will generate an empty sequence, if the difference is greater, the function will throw an error.

Usage

zeq(from, to)

Arguments

from	The lower bound of the sequence
to	The higher bound of the sequence

Value

A sequence ranging from from to to

Examples

# For increasing sequences, zeq() and seq() are identical
zeq(11,15)
zeq(11,11)

# If second argument equals first-1, an empty sequence is returned
zeq(11,10)

# If second argument is less than first-1, the function throws an error
tryCatch(zeq(11,9), error=wrap_error)

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Return the single (unique) value found in a vector

Description

The zingle() function returns the first element in a vector, but only if all the other elements are identical to the first one (the vector only has a zingle value). If the elements are not all identical, it throws an error. The vector must contain at least one non-NA value, or the function errors out as well. This is especially useful in aggregations, when all values in a given group should be identical, but you want to make sure.

Usage

zingle(x, na.rm = FALSE)

Arguments

x	Vector of elements that should all be identical
na.rm	Should NA elements be removed prior to comparison

Details

Optionally takes a na.rm parameter, similarly to sum, mean and other aggregate functions. If TRUE, NA values will be removed prior to comparing the elements, so the function will accept input values that contain a combination of the single value and any NA values (but at least one non-NA value is required).

Only values are tested for equality. Any names are simply ignored, and the result is an unnamed value. This is in line with how other aggregation functions handle names.

Value

The zingle element in the vector

Examples

# If all elements are identical, all is good.
# The value of the element is returned.
zingle(c("Alpha", "Alpha", "Alpha"))

# If any elements differ, an error is thrown
tryCatch(zingle(c("Alpha", "Beta", "Alpha")), error=wrap_error)

if (require("dplyr", quietly=TRUE, warn.conflicts=FALSE)) {
  d <- tibble::tribble(
    ~id, ~name, ~fouls,
    1, "James", 3,
    2, "Jack",  2,
    1, "James", 4
  )

  # If the data is of the correct format, all is good
  d %>%
    dplyr::group_by(id) %>%
    dplyr::summarise(name=zingle(name), total_fouls=sum(fouls))
 }

if (require("dplyr", quietly=TRUE, warn.conflicts=FALSE)) {
  # If a name does not match its ID, we should get an error
  d[1,"name"] <- "Jammes"
  tryCatch({
    d %>%
      dplyr::group_by(id) %>%
      dplyr::summarise(name=zingle(name), total_fouls=sum(fouls))
  }, error=wrap_error)
}

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