使用extract()将数据帧从宽格式改为长格式

我认为你不想使用 extract . 我想 separate 和 spread

library(tidyverse)

df_long <- df_wide %>% 
  gather(key=Category, value=Measurement, Cat1:Cat3_err, factor_key = TRUE) %>%
  separate(Category, into = c("Category", "Type")) %>%
  mutate(Type = ifelse(is.na(Type), "Measurement", "Error")) %>%
  spread(Type, Measurement) %>%
  select(Reading, Category, Measurement, Error, Sample)
df_long
   Reading Category Measurement       Error Sample
1        1     Cat1   0.8453114 0.074961215    X14
2        1     Cat2   4.5962112 0.059012908    X14
3        1     Cat3   5.4100838 0.076049726    X14
4        2     Cat1   4.5956145 0.016215603    X23
5        2     Cat2   1.7768868 0.040258838    X23
6        2     Cat3   1.9597101 0.027356213    X23
7        3     Cat1   1.6204584 0.057760820    X11
8        3     Cat2   4.9478913 0.054855327    X11
9        3     Cat3   2.9670444 0.004276482    X11
10       4     Cat1   0.1831593 0.038415489    X10
11       4     Cat2   2.5716471 0.024932980    X10
12       4     Cat3   8.5517659 0.015378512    X10

也许有一种更快的方法可以做到这一点,但它似乎满足了您的需求:

df_wide %>% 
  gather(key=Category, value=Measurement, Cat1:Cat3_err, factor_key = TRUE) %>%
  extract(Category,c("Meas","Error"),"(Cat\\d)[_]*([a-z]*)")  %>% 
  spread(key = Error, value = Measurement)

注意,除其他事项外,需要使用 \\d 对于R中的正则表达式。