angle {rearrr}

Calculate the angle to an origin

Description

Calculates the angle between each data point (x2, y2) and the origin (x1, y1) with:

atan2(y2 - y1, x2 - x1)

And converts to degrees [0-360), measured counterclockwise from the {x > x1, y = y1} line.

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 finding the angle to e.g. the centroid of each group.

Usage

angle(
  data,
  x_col = NULL,
  y_col = NULL,
  origin = NULL,
  origin_fn = NULL,
  degrees_col_name = ".degrees",
  origin_col_name = ".origin",
  overwrite = FALSE
)

Arguments

data

data.frame or vector.

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.

origin

Coordinates of the origin to calculate angle to. A scalar to use in all dimensions or a vector with one scalar per dimension.

N.B. 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()

degrees_col_name

Name of new column with the degrees.

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 the additional columns (degrees and origin coordinates).

Author(s)

Ludvig Renbo Olsen, [e-mail]

See Also

Other measuring functions: distance(), vector_length()

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(
  "x" = runif(20),
  "y" = runif(20),
  "g" = rep(1:4, each = 5)
)

# Calculate angles in the two dimensions (x and y)
# With the origin at x=0.5, y=0.5
df_angles <- angle(
  data = df,
  x_col = "x",
  y_col = "y",
  origin = c(0.5, 0.5)
)
df_angles

# Plot points with degrees
# Degrees are measured counterclockwise around the
# positive side of the x-axis
if (has_ggplot){
  df_angles %>%
    ggplot(aes(x = x, y = y, color = .degrees)) +
    geom_segment(aes(x = 0.5, xend = 1, y = 0.5, yend = 0.5), color = "magenta") +
    geom_point() +
    theme_minimal()
}

# Calculate angles to the centroid for each group in 'g'
angle(
  data = dplyr::group_by(df, g),
  x_col = "x",
  y_col = "y",
  origin_fn = centroid
)