R语言中使用match函数匹配字符位置返回NA的原因排查

输入类型不匹配 #

strsplit()函数拆分字符串后返回的是列表，但match()只接受向量作为第一个匹配参数。直接用列表去匹配向量，就会返回NA。解决方式是用unlist()把列表转成向量。

存在未匹配的字符 #

原句子拆分后包含空格，但你的alphabet_S里没有空格字符，这部分空格在匹配时自然找不到对应位置，也会返回NA。如果需要匹配空格，得把它加入alphabet_S。

修正后的代码示例 #

sentence <- c("soccer is difficult")
sentence <- tolower(sentence)
# 将strsplit返回的列表转为向量
sentence2 <- unlist(strsplit(sentence, ""))

alphabet_S <- c("a","b","c","d","e","f","g","h","i","j",
                "k","l","m","n","o","p","q","r","s","t",
                "u","v","w","x","y","z","next", " ") # 添加空格

match(sentence2, alphabet_S)

内容的提问来源于stack exchange，提问作者lililililililili