# How to force an error when can't parse value as date in CSV.jl?

**URL:** <https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009>\
**Category:** General Usage\
**Tags:** dates, csv\
**Created:** [November 29, 2022, 7:31pm UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009 "2022-11-29T19:31:18Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![ForceBru](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/forcebru/32/21389_2.png) [@ForceBru](https://discourse.julialang.org/u/ForceBru)\
**Post date:** [November 29, 2022, 7:31pm UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009/1 "2022-11-29T19:31:18Z")

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I’m trying to parse a column in my CSV file as dates, so I try to use `CSV.File(..., dateformat=...)` like this:

```julia
df = CSV.File(
	IOBuffer("Date,Time\n01/01/20, 10:10:10\n01/01/20, 11:11:11\ninvalid, 12:12:12"),
	dateformat=Dict(:Date=>dateformat"dd/mm/yy", :Time=>dateformat"HH:MM:SS"),
	strict=true
) |> DataFrame

```

Clearly, `invalid` is not a valid date. However, this code runs without errors or warnings (even though `strict=true`) and produces a dataframe where the `Date` column is comprised of strings:

```
eltype(df.Date) # InlineStrings.String15

```

How to force an error here?

* * *

I can “fix” this by specifying `types=Dict(:Date=>Dates.Date)` in the call to `CSV.File`, but is it not already clear from the `dateformat` argument that I’d like the `Date` column to contain `Dates.Date`s? So I feel like I’m unnecessarily duplicating my intent to parse dates here…

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<div class="post-metadata">

**Author:** ![quinnj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/quinnj/32/11_2.png) [@quinnj](https://discourse.julialang.org/u/quinnj)\
**Post date:** [November 29, 2022, 8:38pm UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009/2 "2022-11-29T20:38:20Z")

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Part of the issue is that if you specify a `DateFormat` for a specific column, it’s unclear, unless we so some kind of heuristic inspection of the `DateFormat` whether you want a `Date`, `Time`, or `DateTime` for the column type.

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**Author:** ![jar1](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jar1](https://discourse.julialang.org/u/jar1)\
**Post date:** [November 29, 2022, 8:50pm UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009/3 "2022-11-29T20:50:21Z")

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Seems like that inference would be quite effective:

- has a date component and no time component: it’s a date
- has a time component and no date component: it’s a time
- has both: it’s a datetime

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<div class="post-metadata">

**Author:** ![ForceBru](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/forcebru/32/21389_2.png) [@ForceBru](https://discourse.julialang.org/u/ForceBru)\
**Post date:** [November 29, 2022, 10:38pm UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009/4 "2022-11-29T22:38:47Z")

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Why not simply infer all types based on the first row of the CSV file?

1. Try to parse each column of the first (non-header) row.
2. Assign to each column of the overall CSV the types of this first row’s columns.
3. Go on as if the `types` argument to `CSV.File` was set to the types that were inferred from the first row.

I guess special handling of the user-supplied `types` argument will be needed, but the code could again try to fully parse and type the first row, respecting the `types` argument, then fill out types of each column based on the first row and then go to step (3) above.

A very dumb but straightforward algorithm:

1. Run `CSV.File` for the first row of the CSV.
2. Store type information in `first_row_types`.
3. Rerun `CSV.File(..., types= first_row_types)` for the entire file.
4. Bingo, now each column has a type inferred from the first row of the CSV. If some other row doesn’t conform, that’s an error.

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<div class="post-metadata">

**Author:** ![quinnj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/quinnj/32/11_2.png) [@quinnj](https://discourse.julialang.org/u/quinnj)\
**Post date:** [November 30, 2022, 12:40am UTC](https://discourse.julialang.org/t/how-to-force-an-error-when-cant-parse-value-as-date-in-csv-jl/91009/5 "2022-11-30T00:40:40Z")

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You’re certainly welcome to code up your own function that implements your algorithm if it suits your purposes. CSV.jl will indeed respect the types passed from the user and emit warnings for values that don’t parse (or error if `strict=true` is passed).