problems()

• problems()tells us that there was a problem in row 3, col 1 where readr expected a double but got a ..
• So set na = ".".

read_csv(simple_csv, na = ".")

## Rows: 4 Columns: 1
## ── Column specification ────────────────────────────────────────────────────────
## Delimiter: ","
## dbl (1): x
## 
## ℹ Use `spec()` to retrieve the full column specification for this data.
## ℹ Specify the column types or set `show_col_types = FALSE` to quiet this message.

## # A tibble: 4 × 1
##       x
##   <dbl>
## 1    10
## 2    NA
## 3    20
## 4    30