如何在R语言中对42个XY坐标轨迹下采样至11个点？

你需要将42组XY轨迹坐标下采样为11组，R语言里有多种实用方案可以实现：

先修正数据问题 #

你的X坐标向量存在一处语法错误：-0.63-0.64会被解析为-1.27，导致向量长度不符，修正后的数据如下：

x <- c(1.07,0.98,0.90,0.81,0.73,0.65,0.57,0.49,0.41,0.33,0.25,0.17,0.1,0.01,-0.06,
       -0.14,-0.21,-0.28,-0.36,-0.43,-0.49,-0.54,-0.59,-0.63,-0.66,-0.69,-0.72,-0.73,
       -0.72,-0.70,-0.67,-0.64,-0.61,-0.63,-0.64,-0.65,-0.65,-0.65,-0.65,-0.66,-0.66,
       -0.64)
y <- c(-0.11,-0.09,-0.10,-0.12,-0.13,-0.14,-0.19,-0.21,-0.22,-0.24,-0.26,-0.28,-0.30,
       -0.32,-0.34,-0.37,-0.41,-0.45,-0.50,-0.55,-0.61,-0.68,-0.76,-0.84,-0.92,-1.00,
       -1.08,-1.18,-1.28,-1.38,-1.47,-1.56,-1.61,-1.67,-1.73,-1.79,-1.85,-1.91,-1.96,
       -2.02,-2.07)

方法1：基础R均匀索引采样 #

适合要求严格按原始间隔选点的场景：

# 生成11个均匀分布的索引
sample_idx <- round(seq(1, length(x), length.out = 11))
# 提取下采样后的坐标
x_down <- x[sample_idx]
y_down <- y[sample_idx]
# 查看结果
cbind(x_down, y_down)

方法2：插值法下采样（平滑轨迹） #

如果需要更平滑的轨迹效果，用基础R内置的approx函数做线性插值生成指定数量的点：

# 用序列索引模拟轨迹的时间步
t <- 1:length(x)
# 插值生成11个点
downsampled <- approx(t, cbind(x, y), n = 11)
# 提取结果
x_down <- downsampled$y[,1]
y_down <- downsampled$y[,2]
# 查看结果
cbind(x_down, y_down)

方法3：tidyverse生态下的采样 #

若习惯使用dplyr，可将数据转为数据框后操作：

library(dplyr)
# 转为带索引的数据框
traj_df <- tibble(x = x, y = y, idx = 1:n())
# 均匀选取11个点
downsampled_df <- traj_df %>%
  slice(round(seq(1, n(), length.out = 11)))
# 提取坐标
x_down <- downsampled_df$x
y_down <- downsampled_df$y

内容的提问来源于stack exchange，提问作者user20003920