查找图案并过滤开始位置

我想找到图案的位置并过滤位置。

我正在寻找一个函数，用于为每行返回30到34之间的模式“ gaaa”的开始位置。

我解释一下，目前这是函数str_locate_all的结果：

library(stringr)
Sequence <- data.frame(All = c("ggcgaagcagugcucccaguguuuuagagcuagaaauagcaaguuaaaauaaggcuaguccguuaucaacuugaaaaaguggcaccgagucggugcuu",
"aggacaacucgcuccacggccguuuuagagcuagaaauagcaaguuaaaauaaggcuaguccguuaucaacuugaaaaaguggcaccgagucggugcuu",
"cugaaauggcagcagaaacguuuuagagcuagaaauagcaaguuaaaauaaggcuaguccguuaucaacuugaaaaaguggcaccgagucggugcaacaaa",
"ggucaaagaggaggagcucguuuuagagcuagaaauagcaaguuaaaauaaggcuaguccguuaucaacuugaaaaaguggcaccgagucggugcuu"))
str_locate_all(pattern = 'gaaa', Sequence$All)

[[1]]
     start end
[1,]    33  36
[2,]    73  76

[[2]]
     start end
[1,]    34  37
[2,]    74  77

[[3]]
     start end
[1,]     3   6
[2,]    15  18
[3,]    32  35
[4,]    72  75

[[4]]
     start end
[1,]    32  35
[2,]    72  75

结果就是我想要的：

       start
1         33
2         34
3         32
4         32

谢谢！