### Use stringr to process strings

`library(stringr)`

#### 1. Statistical character segment length:

```str_length(c("ab", "R for data science", NA))
#> 2 18 NA```

#### 2. String combination

To combine two or more strings, you can use the str_c() function:

```str_c("x", "y", "z")
#> "xyz"```

You can use the sep parameter to control the separation between strings:

```str_c("x", "y", sep = ", ")
#> "x, y"```

The str_c() function is vectorized, it can automatically loop the short vector so that it has the same length as the longest vector:

```str_c("prefix-", c("a", "b", "c"), "-suffix")
#>  "prefix-a-suffix" "prefix-b-suffix" "prefix-c-suffix"```

To merge character vectors into strings, you can use the collapse() function:

```str_c(c("x", "y", "z"), collapse = ", ")
#>  "x, y, z"```

#### 3. Subset of strings

You can use the str_sub() function to extract part of the string. In addition to string parameters, there are start and end parameters in the str_sub() function, which give the position of the substring (including start and end):

```x <- c("Apple", "Banana", "Pear")
str_sub(x, 1, 3)
#>  "App" "Ban" "Pea"```

Negative number means counting from back to front

```str_sub(x, -3, -1)
#>  "ple" "ana" "ear"```

#### 4. Case conversion

```str_to_upper(c("a", "b"))
#> "A" "B"
str_sub(x, 1, 1) <- str_to_lower(str_sub(x, 1, 1)) x
#>  "apple" "banana" "pear"```
Reference: https://cloud.tencent.com/developer/article/1649279 Use stringr to process strings-Cloud + Community-Tencent Cloud