A Package for Weighted and Unweighted Spatial Centers

## Installation

```
# Install centr from CRAN
install.packages("centr")
# Or the development version from GitHub:
# install.packages("devtools")
devtools::install_github("ryanzomorrodi/centr")
```

## Usage

The main functions are `mean_center`

and `median_center`

. They were designed for calculation of population weighted centroids, but can be extended to other forms of analyses.

Mean center calculates the geographic average center. One can specify the groups to calculate individual centers for groups and weights for each individual point. It is analagous to the ArcGIS Pro Mean Center tool.

```
library(centr)
df <- data.frame(
lon = c(20, 50, 30, 80, 10),
lat = c(25, 70, 30, 50, 30),
grp = c("a", "b", "a", "b", "a"),
wt = c(1, 5, 1, 3, 2)
)
x <- sf::st_as_sf(df, coords = c("lon", "lat"), crs = 4326)
mean_center(x, group = "grp", weight = "wt")
#> Simple feature collection with 2 features and 1 field
#> Geometry type: POINT
#> Dimension: XY
#> Bounding box: xmin: 17.51482 ymin: 29.00224 xmax: 65.92087 ymax: 63.32603
#> Geodetic CRS: WGS 84
#> grp geometry
#> 1 a POINT (17.51482 29.00224)
#> 2 b POINT (65.92087 63.32603)
```

Median center iteratively calculates the point that minimizes distance to all features. One can specify the groups to calculate individual centers for and weights for each individual point. It is analagous to the ArcGIS Pro Median Center tool.

```
library(centr)
df <- data.frame(
lon = c(20, 50, 30, 80, 10),
lat = c(25, 70, 30, 50, 30),
grp = c("a", "b", "a", "b", "a"),
wt = c(1, 5, 1, 3, 2)
)
x <- sf::st_as_sf(df, coords = c("lon", "lat"), crs = 4326)
x_transformed <- sf::st_transform(x, crs = "ESRI:102003")
median_center(x_transformed, group = "grp", weight = "wt")
#> Simple feature collection with 2 features and 1 field
#> Geometry type: POINT
#> Dimension: XY
#> Bounding box: xmin: 4950281 ymin: 4293605 xmax: 8226081 ymax: 8151342
#> Projected CRS: USA_Contiguous_Albers_Equal_Area_Conic
#> grp geometry
#> 1 a POINT (8226081 4293605)
#> 2 b POINT (4950281 8151342)
```