Right now, if you search for a DOI that does not have altmetric data, you get an error "No metrics found for object". Would it be possible for the function to just send a warning when the DOI is not found?

For example, if you do:

altmetrics(doi = "10.22199/s07187475.2015.0001.00004")

You will get:

Error in altmetrics(doi = "10.22199/s07187475.2015.0001.00004") : No metrics found for object

The main issue is that if I want to get the altmetric data for a group of papers, I have to include ways to keep on going when there is an error, so, something like this fails miserably:

DOIS = c("10.22199/s07187475.2015.0001.00004", "10.1093/brain/aww231", "10.1038/s41562-017-0118")
altmetrics_lists = DOIS %>% map( ~ altmetrics(doi = .x))
altmetrics_df = altmetrics_lists %>% map_df(~rAltmetric::altmetric_data(.x))

If I remove the offending DOI, I can get all the altmetric info easily:

DOIS = c("10.1093/brain/aww231", "10.1038/s41562-017-0118")
altmetrics_lists = DOIS %>% map( ~ altmetrics(doi = .x))
altmetrics_df = altmetrics_lists %>% map_df(~rAltmetric::altmetric_data(.x))

As far as I can see, changing: error("No metrics found for object") for warning("No metrics found for object") would suffice?