按行查找数据框中某个值的所有列

Question

我试图在数据框中的每一行中找到具有特定数字的第一列和具有相同值的最后一列。如果数量为 4，请参阅示例数据和所需的输出。

示例数据

ID WZ_1 WZ_2 WZ_3 WZ_4
1  5    4    4    3 
2  4    4    3    3
3  4    4    4    4 

示例输出

ID First Last 
1  WZ_2  WZ_3
2  WZ_1  WZ_2
3  WZ_1  WZ_4 

Answer 1

library(data.table)

# dummy data
# use setDT(df) if yours isn't a datatable already
df <- data.table(id = 1:3
                 , a = c(4,4,0)
                 , b = c(0,4,0)
                 , c = c(4,0,4)
                 ); df
   id a b c
1:  1 4 0 4
2:  2 4 4 0
3:  3 0 0 4

# find 1st & last column with target value
df[, .(id
       , first = apply(.SD, 1, \(i) names(df)[min(which(i==4))])
       , last = apply(.SD, 1, \(i) names(df)[max(which(i==4))])
       )
   ]

Answer 2

使用max.col：

data.frame(ID = df$ID,
           First = names(df)[max.col(df == 4, ties.method = "first")],
           Last = names(df)[max.col(df == 4, ties.method = "last")])

  ID First Last
1  1  WZ_2 WZ_3
2  2  WZ_1 WZ_2
3  3  WZ_1 WZ_4

数据

df <- read.table(header= T, text= "ID WZ_1 WZ_2 WZ_3 WZ_4
1  5    4    4    3 
2  4    4    3    3
3  4    4    4    4 ")

Answer 3

这是一个didyverse选项，我在其中放入了长表格，然后filter仅保留4的值，并且仅保留第一个和最后的出现。然后，我创建一个新列来表示它是第一个值还是最后一个值，然后将其转移回宽格式。

library(tidyverse)

df %>% 
  pivot_longer(-ID) %>% 
  group_by(ID) %>% 
  filter(value == 4) %>% 
  filter(row_number()==1 | row_number()==n()) %>% 
  mutate(col = c("First", "Last")) %>% 
  pivot_wider(names_from = "col", values_from = "name") %>% 
  select(-value)

输出

  <int> <chr> <chr>
1     1 WZ_2  WZ_3 
2     2 WZ_1  WZ_2 
3     3 WZ_1  WZ_4 

数据

df <- structure(list(ID = 1:3, WZ_1 = c(5L, 4L, 4L), WZ_2 = c(4L, 4L, 
4L), WZ_3 = c(4L, 3L, 4L), WZ_4 = c(3L, 3L, 4L)), class = "data.frame", row.names = c(NA, 
-3L))