grep()能对向量中特定条件的元素进行查询，默认return为index。grep()语法与grep()大致相似，但默认return为logical。

参考 ：https://www.jianshu.com/p/11bbfa8e98c5

grep()

代码如下：

grep(pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE,
     fixed = FALSE, useBytes = FALSE, invert = FALSE)

grep()函数参数：

参数	功能
pattern	包含正则表达式的字符串
x	寻找匹配的字符向量，或者可以通过字符向量强制转换的对象。支持长向量
ignore.case	如果为FALSE，则模式匹配区分大小写；如果为TRUE，则在匹配期间忽略大小写
perl	如果为TRUE，使用perl匹配的正则表达式
value	如果为FALSE，则返回包含由grep确定的匹配的索引的向量，如果为TRUE，则返回包含匹配元素本身的向量
fixed	如果为TRUE，则pattern是要按原样匹配的字符串
useBytes	如果为TRUE，则匹配是逐字节而不是逐字符完成的
invert	如果为TRUE，则返回不匹配的元素的索引或值

R 语言中的正则表达式

正则表达式符号	含义
^	匹配一个字符串的开始
$	匹配一个字符串的结尾
.	匹配除了换行符以外的任一字符
*	匹配所有含有*后的字符
?	匹配所有含有?后的字符
+	匹配所有含有+后的字符
.*	可以匹配任意字符
|	表示逻辑的或
[^]	表示逻辑的补集
[]	匹配多个字符，如果不使用任何分隔符号，则搜寻这个集合
[-]	匹配一个范围

贪婪和懒惰规则

默认情况下是匹配尽可能多的字符，是为贪婪匹配，比如sub("a.b","",c("aabab","eabbe"))，默认匹配最长的a开头b结尾的字串，也就是整个字符串。如果要进行懒惰匹配，也就是匹配最短的字串，只需要在后面加个“?”，比如sub("a.?b","",c("aabab","eabbe"))，就会匹配最开始找到的最短的a开头b结尾的字串。

grep()函数实例：

1. ^ 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1')
Results <- grep('^C', Protein, value = T)
Results

image

2. $ 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1')
Results <- grep('2$', Protein, value = T)
Results

image

3. . 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
            'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
            'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
            'GLS','GLS2','NADSYN1')
Results <- grep('MCM.', Protein, value = T)
Results

image

4. * 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1')
Results <- grep('*2', Protein, value = T)
Results

image

5. ? 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('?D', Protein, value = T)
Results

image

6. + 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('+D', Protein, value = T)
Results

image

7. .* 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('T.*3', Protein, value = T)
Results

image

8. | 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('^T|*3', Protein, value = T)
Results

image

9. [^] 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('[^TP53]', Protein, value = T)
Results

image

10. [] 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('[4,3,9,6]', Protein, value = T)
Results

image

11. [-] 的使用：

Protein <- c('TP53','GMPS','CAD','MCM2','MCM3','MCM4',
             'MCM5','MCM6','MCM7','TGM1','TGM2','TGM3',
             'TGM4','TGM5','TGM6','TGM7','CTPS1','CTPS2',
             'GLS','GLS2','NADSYN1','DDB1','DDB2','DAO',
             'DDO','DCLRE1C','DLC1','USP11')
Results <- grep('[1-3]', Protein, value = T)
Results

image