rotate_2d {rearrr}

Rotate the values around an origin in 2 dimensions

Description

The values are rotated counterclockwise around a specified origin.

The origin can be supplied as coordinates or as a function that returns coordinates. The latter can be useful when supplying a grouped data.frame and rotating around e.g. the centroid of each group.

Usage

rotate_2d(
  data,
  degrees,
  x_col = NULL,
  y_col = NULL,
  suffix = "_rotated",
  origin = NULL,
  origin_fn = NULL,
  keep_original = TRUE,
  degrees_col_name = ".degrees",
  origin_col_name = ".origin",
  overwrite = FALSE
)

Arguments

data

data.frame or vector.

degrees

Degrees to rotate values counterclockwise. In [-360, 360]. Can be a vector with multiple degrees.

x_col

Name of x column in `data`. If NULL and `data` is a vector, the index of `data` is used. If `data` is a data.frame, it must be specified.

y_col

Name of y column in `data`. If `data` is a data.frame, it must be specified.

suffix

Suffix to add to the names of the generated columns.

Use an empty string (i.e. "") to overwrite the original columns.

origin

Coordinates of the origin to rotate around. A vector with 2 elements (i.e. origin_x, origin_y). Ignored when `origin_fn` is not NULL.

origin_fn

Function for finding the origin coordinates.

Input: Each column will be passed as a vector in the order of `cols`.

Output: A vector with one scalar per dimension.

Can be created with create_origin_fn() if you want to apply the same function to each dimension.

E.g. `create_origin_fn(median)` would find the median of each column.

Built-in functions are centroid(), most_centered(), and midrange()

keep_original

Whether to keep the original columns. (Logical)

Some columns may have been overwritten, in which case only the newest versions are returned.

degrees_col_name

Name of new column with the degrees. If NULL, no column is added.

origin_col_name

Name of new column with the origin coordinates. If NULL, no column is added.

overwrite

Whether to allow overwriting of existing columns. (Logical)

Details

Applies the following rotation matrix:

[ cos \theta	, -sin \theta	]
[ sin \theta	, cos \theta	]

That is:

x' = x cos \theta - y sin \theta

y' = x sin \theta + y cos \theta

Where \theta is the angle in radians.

As specified at Wikipedia/Rotation_matrix.

Value

data.frame (tibble) with seven new columns containing the rotated x-,y- and z-values and the degrees, radiuses and origin coordinates.

Author(s)

Ludvig Renbo Olsen, [e-mail]

See Also

Other mutate functions: apply_transformation_matrix(), cluster_groups(), dim_values(), expand_distances(), expand_distances_each(), flip_values(), roll_values(), rotate_3d(), shear_2d(), shear_3d(), swirl_2d(), swirl_3d()

Other rotation functions: rotate_3d(), swirl_2d(), swirl_3d()

Examples

# Attach packages
library(rearrr)
library(dplyr)
has_ggplot <- require(ggplot2)  # Attach if installed

# Set seed
set.seed(1)

# Create a data frame
df <- data.frame(
  "Index" = 1:12,
  "A" = c(1:4, 9:12, 15:18),
  "G" = rep(1:3, each = 4)
)

# Rotate values around (0, 0)
rotate_2d(df, degrees = 45, x_col = "Index", y_col = "A", origin = c(0, 0))

# Rotate A around the centroid
df_rotated <- df %>%
  rotate_2d(
    x_col = "Index",
    y_col = "A",
    degrees = c(0, 120, 240),
    origin_fn = centroid
  )
df_rotated

# Plot A and A rotated around overall centroid
if (has_ggplot){
  ggplot(df_rotated, aes(x = Index_rotated, y = A_rotated, color = factor(.degrees))) +
    geom_hline(yintercept = mean(df$A), size = 0.2, alpha = .4, linetype = "dashed") +
    geom_vline(xintercept = mean(df$Index), size = 0.2, alpha = .4, linetype = "dashed") +
    geom_line(alpha = .4) +
    geom_point() +
    theme_minimal() +
    labs(x = "Index", y = "Value", color = "Degrees")
}

# Rotate around group centroids
df_grouped <- df %>%
  dplyr::group_by(G) %>%
  rotate_2d(
    x_col = "Index",
    y_col = "A",
    degrees = c(0, 120, 240),
    origin_fn = centroid
  )
df_grouped

# Plot A and A rotated around group centroids
if (has_ggplot){
  ggplot(df_grouped, aes(x = Index_rotated, y = A_rotated, color = factor(.degrees))) +
    geom_point() +
    theme_minimal() +
    labs(x = "Index", y = "Value", color = "Degrees")
}