find_columns: Find or get columns in a data frame based on search patterns

Description

find_columns() returns column names from a data set that match a certain search pattern, while get_columns() returns the found data. data_select() is an alias for get_columns(), and data_find() is an alias for find_columns().

Usage

find_columns(
  data,
  select = NULL,
  exclude = NULL,
  ignore_case = FALSE,
  regex = FALSE,
  verbose = TRUE,
  ...
)
data_find(
  data,
  select = NULL,
  exclude = NULL,
  ignore_case = FALSE,
  regex = FALSE,
  verbose = TRUE,
  ...
)
data_findcols(
  data,
  pattern = NULL,
  starts_with = NULL,
  ends_with = NULL,
  ignore_case = FALSE,
  ...
)
get_columns(
  data,
  select = NULL,
  exclude = NULL,
  ignore_case = FALSE,
  regex = FALSE,
  verbose = TRUE,
  ...
)
data_select(
  data,
  select = NULL,
  exclude = NULL,
  ignore_case = FALSE,
  regex = FALSE,
  verbose = TRUE,
  ...
)

Value

find_columns() returns a character vector with column names that matched the pattern in select and exclude, or NULL if no matching column name was found. get_columns() returns a data frame with matching columns.

Arguments

data

A data frame.

select

Variables that will be included when performing the required tasks. Can be either

a variable specified as a literal variable name (e.g., column_name),
a string with the variable name (e.g., "column_name"), or a character vector of variable names (e.g., c("col1", "col2", "col3")),
a formula with variable names (e.g., ~column_1 + column_2),
a vector of positive integers, giving the positions counting from the left (e.g. 1 or c(1, 3, 5)),
a vector of negative integers, giving the positions counting from the right (e.g., -1 or -1:-3),
one of the following select-helpers: starts_with(""), ends_with(""), contains(""), a range using : or regex(""),
or a function testing for logical conditions, e.g. is.numeric() (or is.numeric), or any user-defined function that selects the variables for which the function returns TRUE (like: foo <- function(x) mean(x) > 3),
ranges specified via literal variable names, select-helpers (except regex()) and (user-defined) functions can be negated, i.e. return non-matching elements, when prefixed with a -, e.g. -ends_with(""), -is.numeric or -Sepal.Width:Petal.Length. Note: Negation means that matches are excluded, and thus, the exclude argument can be used alternatively. For instance, select=-ends_with("Length") (with -) is equivalent to exclude=ends_with("Length") (no -). In case negation should not work as expected, use the exclude argument instead.

If NULL, selects all columns. Patterns that found no matches are silently ignored, e.g. find_columns(iris, select = c("Species", "Test")) will just return "Species".

exclude

See select, however, column names matched by the pattern from exclude will be excluded instead of selected. If NULL (the default), excludes no columns.

ignore_case

Logical, if TRUE and when one of the select-helpers or a regular expression is used in select, ignores lower/upper case in the search pattern when matching against variable names.

regex

Logical, if TRUE, the search pattern from select will be treated as regular expression. When regex = TRUE, select must be a character string (or a variable containing a character string) and is not allowed to be one of the supported select-helpers or a character vector of length > 1. regex = TRUE is comparable to using one of the two select-helpers, select = contains("") or select = regex(""), however, since the select-helpers may not work when called from inside other functions (see 'Details'), this argument may be used as workaround.

verbose

Toggle warnings.

...

Arguments passed down to other functions. Mostly not used yet.

pattern

A regular expression (as character string), representing the pattern to be matched in the in column names. Can also be one of the following select-helpers: starts_with(""), end_with(""), regex(""), contains(""), or a range using :.

starts_with, ends_with

Character string, containing the string to be matched in the column names. starts_with finds matches at the beginning of column names, ends_with finds matches at the end of column names.

Details

Note that there are some limitations when calling this from inside other functions. The following will work as expected, returning all columns that start with "Sep":

foo <- function(data) {
  find_columns(data, select = starts_with("Sep"))
}
foo(iris)

However, this example won't work as expected!

foo <- function(data) {
  i <- "Sep"
  find_columns(data, select = starts_with(i))
}
foo(iris)

One workaround is to use the regex argument, which provides at least a bit more flexibility than exact matching. regex in its basic usage (as seen below) means that select behaves like the contains("") select-helper, but can also make the function more flexible by allowing to define complex regular expression pattern in select.

foo <- function(data) {
  i <- "Sep"
  find_columns(data, select = i, regex = TRUE)
}
foo(iris)

Examples

Run this code

# Find columns names by pattern
find_columns(iris, starts_with("Sepal"))
find_columns(iris, ends_with("Width"))
find_columns(iris, regex("\\."))
find_columns(iris, c("Petal.Width", "Sepal.Length"))

# starts with "Sepal", but not allowed to end with "width"
find_columns(iris, starts_with("Sepal"), exclude = contains("Width"))

# find numeric with mean > 3.5
numeric_mean_35 <- function(x) is.numeric(x) && mean(x, na.rm = TRUE) > 3.5
find_columns(iris, numeric_mean_35)