Why is there no progress bar in dlply (in the R plyr package)

Question

I am using the plyr package to process lists and data frames. I have noticed the following behaviour:

Example 1 -

list_2 <- llply(list_1, function_1, .progress='text')

this works as expected. It generates list_2 from list_1 with function_1 applied to each list_1 element and I see the progress bar.

Example 2 -

list_3 <- dlply(list_2, function_2, .progress='text')

this also works insofar as I get the results in list_3 that I expect, however, I do not get a progress bar.

In summary, why does the progress bar not work for dlply but works for llply. (It also works for ldply).

Answer 1

Because you're not splitting your data.frame on anything. If your second example was:

list_3 <- dlply(df_2, .(colname2), function_2, .progress='text')

then it would work. The progress meter in plyr is based on the number of chunks completed.