如何按特定条件删除 data.frame 中的行？答案

【问题标题】：How to delete rows in a data.frame by a specific condition?如何按特定条件删除 data.frame 中的行？
【发布时间】：2020-11-18 22:30:44
【问题描述】：

我尝试删除 data.frame 中的一些行，但无法解决问题。有人可以帮忙吗？

这是data.frame

   subj trial fix type
1     a     1   1    K
2     a     1   2    T
3     a     1   3    T
4     a     2   1    K
5     a     2   2    K
6     a     2   3    T
7     b     1   1    T
8     b     1   2    K
9     b     1   3    K
10    b     2   1    K
11    b     2   2    T
12    b     2   3    T

并且我希望对于每个主题，在每个试验中 T 第一次出现的行。结果应如下所示：

   subj trial fix type
2     a     1   2    T
6     a     2   3    T
7     b     1   1    T
11    b     2   2    T

【问题讨论】：

标签： r for-loop if-statement apply

【解决方案1】：

使用来自dplyr 的slice 的一个想法，

library(dplyr)

df %>% 
 group_by(subj, trial) %>% 
 slice(which(type == 'T')[1])

# A tibble: 4 x 4
# Groups:   subj, trial [4]
#  subj  trial   fix type 
#  <fct> <int> <int> <fct>
#1 a         1     2 T    
#2 a         2     3 T    
#3 b         1     1 T    
#4 b         2     2 T

【讨论】：

很好的答案！作为补充，slice(which.max(type == 'T')) 也可以。

【解决方案2】：

您可以使用filter() + distinct()。

library(dplyr)

df %>%
  filter(type == "T") %>%
  distinct(subj, trial, .keep_all = T)

#    subj trial fix type
# 2     a     1   2    T
# 6     a     2   3    T
# 7     b     1   1    T
# 11    b     2   2    T

数据

df <- structure(list(subj = c("a", "a", "a", "a", "a", "a", "b", "b", 
"b", "b", "b", "b"), trial = c(1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 
1L, 2L, 2L, 2L), fix = c(1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 
1L, 2L, 3L), type = c("K", "T", "T", "K", "K", "T", "T", "K", 
"K", "K", "T", "T")), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"))

【讨论】：

【解决方案3】：

我们可以使用slice 和match

library(dplyr)
df %>% 
     group_by(subj, trial) %>%
     slice(match('T', type))
# A tibble: 4 x 4
# Groups:   subj, trial [4]
#  subj  trial   fix type 
#  <chr> <int> <int> <chr>
#1 a         1     2 T    
#2 a         2     3 T    
#3 b         1     1 T    
#4 b         2     2 T

数据

df <- structure(list(subj = c("a", "a", "a", "a", "a", "a", "b", "b", 
"b", "b", "b", "b"), trial = c(1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 
1L, 2L, 2L, 2L), fix = c(1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 
1L, 2L, 3L), type = c("K", "T", "T", "K", "K", "T", "T", "K", 
"K", "K", "T", "T")), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12"))

【讨论】：