# dlply

From plyr v1.8.3
by Hadley Wickham

##### Split data frame, apply function, and return results in a list.

For each subset of a data frame, apply function then combine results into a
list. `dlply`

is similar to `by`

except that the results
are returned in a different format.
To apply a function for each row, use `alply`

with
`.margins`

set to `1`

.

- Keywords
- manip

##### Usage

```
dlply(.data, .variables, .fun = NULL, ..., .progress = "none",
.inform = FALSE, .drop = TRUE, .parallel = FALSE, .paropts = NULL)
```

##### Arguments

- .data
- data frame to be processed
- .variables
- variables to split data frame by, as
`as.quoted`

variables, a formula or character vector - .fun
- function to apply to each piece
- ...
- other arguments passed on to
`.fun`

- .progress
- name of the progress bar to use, see
`create_progress_bar`

- .inform
- produce informative error messages? This is turned off by default because it substantially slows processing speed, but is very useful for debugging
- .drop
- should combinations of variables that do not appear in the input data be preserved (FALSE) or dropped (TRUE, default)
- .parallel
- if
`TRUE`

, apply function in parallel, using parallel backend provided by foreach - .paropts
- a list of additional options passed into
the
`foreach`

function when parallel computation is enabled. This is important if (for example) your code relies on external data or packages: use the`.e`

##### Value

- list of results

##### Input

This function splits data frames by variables.

##### Output

If there are no results, then this function will return
a list of length 0 (`list()`

).

##### References

Hadley Wickham (2011). The Split-Apply-Combine Strategy
for Data Analysis. Journal of Statistical Software, 40(1), 1-29.

##### See Also

##### Examples

```
linmod <- function(df) {
lm(rbi ~ year, data = mutate(df, year = year - min(year)))
}
models <- dlply(baseball, .(id), linmod)
models[[1]]
coef <- ldply(models, coef)
with(coef, plot(`(Intercept)`, year))
qual <- laply(models, function(mod) summary(mod)$r.squared)
hist(qual)
```

*Documentation reproduced from package plyr, version 1.8.3, License: MIT + file LICENSE*

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