shear_2d {rearrr}

Shear the values around an origin in 2 dimensions

Description

Shear a set of 2d points around an origin. The shearing formulas (excluding the origin movements) is:

x' = x + x_shear * y

y' = y + y_shear * x

The data points in `data` are moved prior to the shearing, to bring the origin to 0 in all dimensions. After the shearing, the inverse move is applied to bring the origin back to its original position.

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 shearing around e.g. the centroid of each group.

Usage

shear_2d(
  data,
  x_shear,
  y_shear = 0,
  x_col = NULL,
  y_col = NULL,
  suffix = "_sheared",
  origin = NULL,
  origin_fn = NULL,
  keep_original = TRUE,
  shear_col_name = ".shear",
  origin_col_name = ".origin",
  overwrite = FALSE
)

Arguments

data

data.frame or vector.

x_shear

Shear factor for the x dimension (numeric). Decides the amount of shearing. Can be a vector with multiple shear factors.

y_shear

Shear factor for the y dimension (numeric). Decides the amount of shearing. Can be a vector with multiple shear factors.

x_col

Name of x column in `data`.

y_col

Name of y column in `data`.

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 shear around. Vector with 2 elements (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.

shear_col_name

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

Also adds a string version with the same name + "_str", making it easier to group by the shearing factors when plotting multiple shearings.

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)

Value

data.frame (tibble) with sheared columns, the shearing factors and the 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_2d(), rotate_3d(), shear_3d(), swirl_2d(), swirl_3d()

Other shearing functions: shear_3d()

Examples

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

# Create a data frame
df <- data.frame(
  "x" = rep(1:6, each = 2),
  "y" = rep(c(1, 4), 6),
  "g" = rep(1:2, each = 6)
)

# Shear the x variable with regards to y
# around the centroid
df_sheared <- shear_2d(
  data = df,
  x_shear = 2.5,
  x_col = "x",
  y_col = "y",
  origin_fn = centroid
)

# Plot sheared data
# Black: original points
# Red: sheared points
if (has_ggplot){
  df_sheared %>%
    ggplot(aes(x = x, y = y)) +
    geom_point() +
    geom_point(aes(x = x_sheared, y = y_sheared, color = "red")) +
    theme_minimal()
}

# Shear in both dimensions
df_sheared <- shear_2d(
  data = df,
  x_shear = 2.5,
  y_shear = 2.5,
  x_col = "x",
  y_col = "y",
  origin_fn = centroid
)

# Plot sheared data
# Black: original points
# Red: sheared points
if (has_ggplot){
  df_sheared %>%
    ggplot(aes(x = x, y = y)) +
    geom_point() +
    geom_point(aes(x = x_sheared,y = y_sheared, color = "red")) +
    theme_minimal()
}

# Shear grouped data frame
# Affects the calculated origin
df_sheared <- shear_2d(
  data = dplyr::group_by(df, g),
  x_shear = 2.5,
  x_col = "x",
  y_col = "y",
  origin_fn = centroid
)

# Plot sheared data
# Black: original points
# Red: sheared points
if (has_ggplot){
  df_sheared %>%
    ggplot(aes(x = x, y = y)) +
    geom_point() +
    geom_point(aes(x = x_sheared, y = y_sheared, color = "red")) +
    theme_minimal()
}

# Shear a vector with multiple shearing factors
shear_2d(
  data = c(1:10),
  x_shear = c(1, 1.5, 2, 2.5),
  origin = c(0, 0)
)