Package 'polypoly'

Add orthogonal polynomial columns to a dataframe

Description

Add orthogonal polynomial columns to a dataframe

Usage

poly_add_columns(
  .data,
  .col,
  degree = 1,
  prefix = NULL,
  scale_width = NULL,
  na_values = c("error", "warn", "allow")
)

Arguments

.data	a dataframe
.col	a bare column name
degree	number of polynomial terms to add to the dataframe
prefix	prefix for the names to add to the dataframe. default is the name of .col.
scale_width	optionally rescale the dataframe using poly_rescale(). Default behavior is not to perform any rescaling.
na_values	How to handle missing values. Default is "error" which raises an error. Other options include "warn" to raise a warning and "allow" to silently accept missing values.

Value

the dataframe with additional columns of orthogonal polynomial terms of .col

Examples

df <- data.frame(time = rep(1:5, 3), y = rnorm(15))

# adds columns "time1", "time2", "time3"
poly_add_columns(df, time, degree = 3)

# adds columns "t1", "t2", "t3 and rescale
poly_add_columns(df, time, degree = 3, prefix = "t", scale_width = 1)

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Melt a polynomial matrix

Description

Melt a polynomial matrix

Usage

poly_melt(x)

Arguments

x	a matrix created by stats::poly()

Details

The degree values are returned as a character vector because they should be treated categorically (as when plotting). Moreover, matrices made with multiple vectors (e.g., poly(rnorm(10), rnorm(10), degree = 2)) have names that are not numerically meaningful (e.g., 1.0, 2.0, 0.1, 1.1, 0.2),

Value

a tibble::tibble() with three columns: observation (row number of the matrix), polynomial degree, and value.

Examples

m <- poly(rnorm(10), degree = 3)
poly_melt(m)

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Plot a polynomial matrix

Description

Plot a polynomial matrix

Usage

poly_plot(x, by_observation = TRUE, x_col = 1)

poly_plot_data(x, by_observation = TRUE, x_col = 1)

Arguments

x	a matrix created by stats::poly()
by_observation	whether the x axis should be mapped to the observation/row number (TRUE, the default) or to the degree-1 terms of the matrix (FALSE)
x_col	integer indicating which column to plot as the x-axis when by_observation is FALSE. Default is 1 (assumes the first column is the linear polynomial term).

Value

a ggplot2::ggplot() plot of the degree terms from the matrix. For poly_plot_data(), the dataframe used to create the plot is returned instead.

Examples

# Defaults to plotting using the row number as x-axis
m <- poly(1:100, degree = 3)
poly_plot(m)

# Not good because observations were not sorted
m2 <- poly(rnorm(100), degree = 3)
poly_plot(m2)

# Instead set by_observation to FALSE to plot along the degree 1 values
poly_plot(m2, by_observation = FALSE)

# Get a dataframe instead of plot
poly_plot_data(m2, by_observation = FALSE)

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Rescale the range of a polynomial matrix

Description

Rescale the range of a polynomial matrix

Usage

poly_rescale(x, scale_width = 1)

Arguments

x	a matrix created by stats::poly()
scale_width	the desired range (max - min) for the first column of the matrix

Details

This function strips away the poly class and the coefs attribute of the matrix. This is because those attributes no longer describe the transformed matrix.

Value

the rescaled polynomial matrix (as a plain matrix with coefs attribute removed)

Examples

m <- poly(1:10, degree = 4)

# Difference between min and max values of first column is 10
scaled <- poly_rescale(m, scale_width = 10)
scaled

# Rescaled values are still orthogonal
zapsmall(cor(scaled))

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polypoly: Helper functions for orthogonal polynomials

Description

This package provides helpful functions for orthogonal polynomials created by stats::poly(). These include plotting poly_plot(), tidying poly_melt(), rescaling poly_rescale(), and manipulating a dataframe poly_add_columns().

Author(s)

Tristan Mahr

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