Question: I want to filter some posts from data.I try to use this code but it don't work.It run out `post.frontmatter.title.filter is not a function`

```
{posts.map((post, index) => (
 post.frontmatter.title.filter(name=>name.includes('J')).map(filterdtitle=>(
<li>{filterdtitle}</li>
))
))}

```

I get the data of posts by getStaticProps like this and then I pass the posts to the function.The posts include title.I can get by {post.frontmatter.title},it is working.

```
 const { data: frontmatter } = matter(markdownWithMeta)

    return {
      slug,
      frontmatter
    }
  })

```

I want to know that how make it work.Thank you

Answer: 
I believe you need to rewrite your code like this.

1. the title is a string, and the filter doesn't support string
2. you added an extra step by using a filter and include in the same line for a title.

---

```
     {
      posts.filter((post, index) =>   
 post.frontmatter.title.includes('K')).map((k)=><li>{k.frontmatter.title}</li>)
        }

```
Looks like `title` is a string. `filter()` method is available only for array.