changed: Identify changed values

Description

The changed function identifies changes in a vector or data frame. The function is used to locate grouping boundaries. It will return a TRUE each time the current value is different from the previous value. The changed function is similar to the Base R duplicated function, except the changed function will return TRUE even if the changed value is not unique.

Usage

changed(x, reverse = FALSE, simplify = FALSE)

Value

A vector of TRUE or FALSE values indicating the grouping boundaries of the vector or data frame. If the input data is a data frame and the "simplify" parameter is FALSE, the return value will be a data frame of logical vectors describing changed values for each column.

Arguments

x: A vector of values in which to identify changed values. Also accepts a data frame. In the case of a data frame, the function will use all columns. Input data can be any data type.
reverse: Reverse the direction of the scan to identify the last value in a group instead of the first.
simplify: If the input data to the function is a data frame, the simplify option will return a single vector of indicator values instead of a data frame of indicator values.

Details

For a data frame, by default, the function will return another data frame with an equal number of change indicator columns. The column names will be the original column names, with a ".changed" suffix.

To collapse the multiple change indicators into one vector, use the "simplify" option. In this case, the returned vector will essentially be an "or" operation across all columns.

Examples

Run this code

# Create sample vector
v1 <- c(1, 1, 1, 2, 2, 3, 3, 3, 1, 1)

# Identify changed values
res1 <- changed(v1)

# View results
res1
# [1] TRUE FALSE FALSE  TRUE FALSE  TRUE FALSE FALSE  TRUE FALSE

# Create sample data frame
v2 <- c("A", "A", "A", "A", "A", "A", "B", "B", "B", "B")
dat <- data.frame(v1, v2)

# View original data frame
dat
#    v1 v2
# 1   1  A
# 2   1  A
# 3   1  A
# 4   2  A
# 5   2  A
# 6   3  A
# 7   3  B
# 8   3  B
# 9   1  B
# 10  1  B

# Get changed values for each column
res2 <- changed(dat)

# View results
res2
#    v1.changed v2.changed
# 1        TRUE       TRUE
# 2       FALSE      FALSE
# 3       FALSE      FALSE
# 4        TRUE      FALSE
# 5       FALSE      FALSE
# 6        TRUE      FALSE
# 7       FALSE       TRUE
# 8       FALSE      FALSE
# 9        TRUE      FALSE
# 10      FALSE      FALSE

# Get changed values for all columns
res3 <- changed(dat, simplify = TRUE)

# View results
res3
# [1] TRUE FALSE FALSE  TRUE FALSE  TRUE  TRUE FALSE  TRUE FALSE

# Get last items in each group instead of first
res4 <- changed(dat, reverse = TRUE)

# View results
res4
#    v1.changed v2.changed
# 1       FALSE      FALSE
# 2       FALSE      FALSE
# 3        TRUE      FALSE
# 4       FALSE      FALSE
# 5        TRUE      FALSE
# 6       FALSE       TRUE
# 7       FALSE      FALSE
# 8        TRUE      FALSE
# 9       FALSE      FALSE
# 10       TRUE       TRUE