r - 是否需要使用 awk 预处理文件，还是可以直接在 R 中完成？

Question

我曾经用 awk 处理 csv 文件，这是我的第一个脚本:

tail -n +2 shifted_final.csv | awk -F, 'BEGIN {old=$2} {if($2!=old){print $0; old=$2;}}' | less

此脚本在第 2 列中查找重复值(如果第 n 行的值与第 n+1、n+2 ... 行的值相同)并仅打印第一次出现。例如，如果您提供以下输入:

ord,orig,pred,as,o-p
1,0,0,1.0,0
2,0,0,1.0,0
3,0,0,1.0,0
4,0,0,0.0,0
5,0,0,0.0,0
6,0,0,0.0,0
7,0,0,0.0,0
8,0,0,0.0,0
9,0,0,0.0,0
10,0,0,0.0,0
11,0,0,0.0,0
12,0,0,0.0,0
13,0,0,0.0,0
14,0,0,0.0,0
15,0,0,0.0,0
16,0,0,0.0,0
17,0,0,0.0,0
18,0,0,0.0,0
19,0,0,0.0,0
20,0,0,0.0,0
21,0,0,0.0,0
22,0,0,0.0,0
23,4,0,0.0,4
24,402,0,1.0,402
25,0,0,1.0,0

然后输出将是:

1,0,0,1.0,0
23,4,0,0.0,4
24,402,0,1.0,402
25,0,0,1.0,0

编辑:
我让添加第二个脚本有点困难:

第二个脚本执行相同的操作，但打印最后一次重复出现:

tail -n +2 shifted_final.csv | awk -F, 'BEGIN {old=$2; line=$0} {if($2==old){line=$0}else{print line; old=$2; line=$0}} END {print $0}' | less

它的输出将是:

22,0,0,0.0,0
23,4,0,0.0,4
24,402,0,1.0,402
25,0,0,1.0,0

我认为 R 是应该处理此类任务的强大语言，但我发现只有有关从 R 等调用 awk 脚本的问题。如何在 R 中执行此操作？

Answer 1

关于您的问题的更新，一个更通用的解决方案，感谢@nicola:

Idx.first <- c(TRUE, tbl$orig[-1] != tbl$orig[-nrow(tbl)])
##
R> tbl[Idx.first,]
#    ord orig pred as o.p
# 1    1    0    0  1   0
# 23  23    4    0  0   4
# 24  24  402    0  1 402
# 25  25    0    0  1   0

如果您想使用 最后 在运行中出现一个值，而不是 第一 , 只需追加 TRUE到@nicola 的索引表达式，而不是在前面添加它:

Idx.last <- c(tbl$orig[-1] != tbl$orig[-nrow(tbl)], TRUE)
##
R> tbl[Idx.last,]
#    ord orig pred as o.p
# 22  22    0    0  0   0
# 23  23    4    0  0   4
# 24  24  402    0  1 402
# 25  25    0    0  1   0

无论哪种情况， tbl$orig[-1] != tbl$orig[-nrow(tbl)]将第 2 列中的第 2 到第 n 个值与第 2 列中的第 1 到 n-1 个值进行比较。结果是一个逻辑向量，其中 TRUE元素表示连续值的变化。由于比较的长度为 n-1，因此推送额外的 TRUE前面的值(情况 1)将选择运行中的第一次出现，同时添加额外的 TRUE到后面(情况 2)将选择运行中的最后一个事件。

数据:

tbl <- read.table(text = "ord,orig,pred,as,o-p
1,0,0,1.0,0
2,0,0,1.0,0
3,0,0,1.0,0
4,0,0,0.0,0
5,0,0,0.0,0
6,0,0,0.0,0
7,0,0,0.0,0
8,0,0,0.0,0
9,0,0,0.0,0
10,0,0,0.0,0
11,0,0,0.0,0
12,0,0,0.0,0
13,0,0,0.0,0
14,0,0,0.0,0
15,0,0,0.0,0
16,0,0,0.0,0
17,0,0,0.0,0
18,0,0,0.0,0
19,0,0,0.0,0
20,0,0,0.0,0
21,0,0,0.0,0
22,0,0,0.0,0
23,4,0,0.0,4
24,402,0,1.0,402
25,0,0,1.0,0",
header = TRUE,
sep = ",")