使用gsub和适当的正则表达式，不需要附加包。

df[2:3] <- lapply(df[2:3], \(x) as.numeric(gsub('\\[|\\]', '', x)))
df
#   participant position_1 position_2
# 1         s07 -3.9600245 -6.4007552
# 2         s08 -2.4331781 -2.2651470
# 3         s10  0.5703462 -0.9808197
# 4         s11 -2.9355256 -2.9176683

• 数据：*

df <- structure(list(participant = c("s07", "s08", "s10", "s11"), position_1 = c("[-3.96002452]", 
"[-2.43317811]", "[0.57034622]", "[-2.93552563]"), position_2 = c("[-6.40075519]", 
"[-2.26514695]", "[-0.98081968]", "[-2.91766826]")), class = "data.frame", row.names = c(NA, 
-4L))

使用readr包中的parse_number()：

library(tidyverse)

# the data
participant <-c("s07", "s08", "s10", "s11")
position_1 <- c("[-3.96002452]", "[-2.43317811]" ,"[0.57034622]", "[-2.93552563]")
position_2 <- c("[-6.40075519]", "[-2.26514695]", "[-0.98081968]" ,"[-2.91766826]" )

df <- tibble(participant, position_1, position_2)

# the code
df %>% 
  mutate(across(-participant, ~parse_number(.)))

participant position_1 position_2
  <chr>            <dbl>      <dbl>
1 s07             -3.96      -6.40 
2 s08             -2.43      -2.27 
3 s10              0.570     -0.981
4 s11             -2.94      -2.92

example <- c("[-3.96002452]" ,"[-2.43317811]" ,"[0.57034622]", "[-2.93552563]")
readr::parse_number(example)

[1] -3.9600245 -2.4331781  0.5703462 -2.9355256

使用readr包（如果没有，请安装）。