Why does ymd() return “All formats failed to parse” in mutate()?

R code
1

Hi everyone,

I was trying to clean a small dataset and convert the onset_date column to class Date using ymd() from lubridate. However, I got the following warning:

Warning message:
There was 1 warning in mutate().
:information_source: In argument: onset_date = ymd(onset_date).
Caused by warning:
! All formats failed to parse. No formats found.

Could someone please explain why ymd() fails to parse these dates and how to fix it?

2

Hello,

Without a reproducible example, it’s hard to know for sure. I suspect it’s due to the dates in the data having a different format than the YYYY-mm-dd format that the ymd function expects. If your date is of the form mm-dd-YYYY then you should use the mdy function.

Here is an example:

# loading packages
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union
library(tibble)

# creating fake data
fake_data <- tibble(
  date_1 = c("2025-01-01", "2025-01-02", "2025-01-03", "2025-01-04", "2025-01-05"),
  date_2 = c("01/01/25", "01/02/25", "01/03/25", "01/04/25", "01/05/25")
)

# converting the dates
fake_data |>
  mutate(
    date_1 = ymd(date_1),
    date_2 = mdy(date_2)
  )
#> # A tibble: 5 × 2
#>   date_1     date_2    
#>   <date>     <date>    
#> 1 2025-01-01 2025-01-01
#> 2 2025-01-02 2025-01-02
#> 3 2025-01-03 2025-01-03
#> 4 2025-01-04 2025-01-04
#> 5 2025-01-05 2025-01-05

Created on 2025-10-16 with reprex v2.1.1

Session info

 
sessioninfo::session_info()
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#>  version  R version 4.5.1 (2025-06-13)
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#>  date     2025-10-16
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#>  lifecycle     1.0.4   2023-11-07 [1] RSPM
#>  lubridate   * 1.9.4   2024-12-08 [1] RSPM
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#> 
#>  [1] /Users/timothychisamore/Library/R/x86_64/4.5/library
#>  [2] /Library/Frameworks/R.framework/Versions/4.5-x86_64/Resources/library
#>  * ── Packages attached to the search path.
#> 
#> ──────────────────────────────────────────────────────────────────────────────

All the best,

Tim

3

Thanks for the explanation! Here’s the reprex — I forgot to attach it to the post.

reprex 2

install and load packages

pacman::p_load(rio, here, janitor, tidyverse, reprex, datapasta)

import data

surv_raw ← data.frame(stringsAsFactors = FALSE,
case_id = c(“694928”,“86340d”,“92d002”,“544bd1”,“6056ba”),
sex = c(“m”, “f”, “f”, “f”, “f”),
onset_date = c(“11/9/2014”,“10/30/2014”,“8/16/2014”,“8/29/2014”,“10/20/2014”))

try to convert column to class “Date”

surv_clean ← surv_raw %>%
clean_names() %>%
mutate(onset_date = ymd(onset_date))

check the CLEANED date column class and date range

class(surv_clean$onset_date)
range(surv_clean$onset_date)

4

Hello,

Please see my previous response about the format of your date variable, that is what is causing your error.

All the best,

Tim

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