`pins::pin_write` Error: Writing Pins Without Versioning

Encountering errors while using the pins package in R can be frustrating, especially when writing pins to a local board. One common issue arises when the pin_write function fails due to a missing versioned input argument. This article delves into why this error occurs, how to resolve it, and provides a comprehensive understanding of how to effectively use pins::pin_write for your data management needs. Let’s explore this issue and ensure your data pinning process is smooth and efficient.

The Problem: pins::pin_write Fails

When using the pins package, you might encounter an error when attempting to write a pin to a local board. This typically occurs when the versioned argument is not explicitly specified. Let's break down the error, understand the cause, and explore solutions to ensure your data is pinned correctly.

Detailed Explanation of the Error

The error message usually looks like this:

Guessing `type = 'rds`'
Error in versioned || n_versions == 0 : invalid 'x' type in 'x || y'

This error arises from the internal logic of the pins::pin_write function, particularly when it tries to determine whether to create a new version of the pin. Without the versioned argument, the function struggles to handle the versioning process, leading to the “invalid ‘x’ type in ‘x || y’” error. The traceback often points to issues within the pin_meta() function, indicating that the system cannot find the pin metadata because of the versioning ambiguity.

Why Does This Happen?

The pins package is designed to manage data pins, which can be versioned to track changes over time. When writing a pin, the package needs to know whether to treat the pin as versioned or not. If versioned is not specified, the function's internal logic can falter, especially when dealing with local boards where versioning might not be the default behavior. This is why explicitly setting versioned = TRUE often resolves the issue.

Minimal Working Example (MWE)

To illustrate the problem, consider this minimal working example (MWE):

local_board <- pins::board_local(here::here())

pins::pin_write(
 board = local_board,
 x = head(iris),
 name = "iris_head"
)

This code snippet attempts to write the first few rows of the iris dataset to a local board named “iris_head.” Without the versioned argument, this code will likely produce the aforementioned error. The error message suggests an issue with the type check within the versioning logic, as highlighted in the traceback.

Error Traceback

The rlang::last_trace() function provides a detailed traceback, which can help pinpoint the exact location of the error. Here's an example of what the traceback might look like:

<error/pins_pin_missing>
Error in `pin_meta()`:
! Can't find pin called "iris_head"
ℹ Use `pin_list()` to see all available pins in this board
---
Backtrace:
 ▆
 1. └─pins::pin_read(local_board, "iris_head")
 2. ├─pins::pin_fetch(board, name, version = version, ...)
 3. └─pins:::pin_fetch.pins_board_folder(...)
 4. │ ├─pins::pin_meta(board, name, version = version)
 5. │ └─pins:::pin_meta.pins_board_folder(board, name, version = version)
Run rlang::last_trace(drop = FALSE) to see 4 hidden frames.

This traceback indicates that the error occurs within the pin_meta() function, which is responsible for retrieving pin metadata. The message “Can’t find pin called ‘iris_head’” suggests that the function cannot locate the pin's metadata, likely due to the versioning issue.

The Solution: Specifying versioned = TRUE

The primary solution to this issue is to explicitly set the versioned argument to TRUE when calling pins::pin_write. This tells the function to treat the pin as versioned, ensuring that it handles the versioning logic correctly.

Corrected Code

Here’s the corrected code snippet:

pins::pin_write(
 board = local_board,
 x = head(iris),
 name = "iris_head",
 versioned = TRUE
)

By adding versioned = TRUE, the function now knows to create a new version for the pin. This resolves the error and allows the pin to be written successfully. The output confirms that a new version is being created:

Guessing `type = 'rds`'
Creating new version '20251129T081129Z-71d62'
Writing to pin 'iris_head'

Understanding Versioning

Versioning is a crucial feature of the pins package, allowing you to track changes to your data over time. When versioned = TRUE, each time you write a pin with the same name, a new version is created. This is particularly useful for maintaining a history of your data, enabling you to revert to previous states if needed. If versioning is not necessary, setting versioned = FALSE might be appropriate, but in many cases, explicitly enabling versioning ensures smoother operation.

Additional Considerations and Best Practices

While setting versioned = TRUE resolves the immediate error, there are additional considerations and best practices to keep in mind when working with the pins package.

Explicitly Setting type

While pins::pin_write can often guess the data type, explicitly setting the type argument can prevent unexpected behavior. For example:

pins::pin_write(
 board = local_board,
 x = head(iris),
 name = "iris_head",
 type = "rds",
 versioned = TRUE
)

Here, `type =