`## Loading required package: convey`

`## Loading required package: laeken`

I don’t expect this vignette to be help for most srvyr users, it is
instead intended for other package developers. An exciting new feature
that is easier now that I have reworked srvyr’s non-standard evaluation
to match dplyr 0.7+ is that it is now possible for non-srvyr functions
to be called from within `summarize`

. This vignette describes
some of the inner-workings of summarize so that others can extend srvyr.
This is kind of a fiddly part of srvyr, and I don’t expect that many
people will want or need to understand it, so this guide is mostly aimed
at package authors who already have an understanding of how survey
objects work. If you’d like more explanation, please let me know on github!

This guide has also been rewritten for srvyr 1.0, as I had to rework summarize and was unable to maintain backwards compatibility.

srvyr implements the “survey statistics” functions from the survey
package. Some examples are the svymean, svytotal, svyciprop, svyquantile
and svyratio all return a `svystat`

object which usually
prints out the estimate and its standard error and other estimates of
the variance can be calculated from it. In srvyr, these estimates are
created inside of a summarize call and the variance estimates are
specified at the same time.

The combination of srvyr’s group_by and summarize is analogous to the
`svyby`

function that performs one of the survey statistic
function and performs it on multiple groups. However, as of srvyr 1.0,
srvyr no longer uses `svyby`

, instead the survey object is
split into each group’s

srvyr’s summarize expects that the survey statistics functions will return objects that are formatted in a particular way. Below, I’ll explain some of the functions that will help create these objects for you in most cases, but the return should be:

- A
`srvyr_result_df`

object (which is just a wrapper around a`data.frame`

) - Generally there should be 1 row for ungrouped, or 1 row per group, but this is no longer required.
- The names are based on the argument name from the summarize call but this name can’t provided to the functions. Instead, summarize does the renaming and your function should name the variables “coef” (which is renamed to the parameter name) or with a suffix that will be appended after the parameter name.

srvyr now exports several functions that can help convert functions designed for the survey package to this format.

`cur_svy()`

- This function, modeled after`dplyr::current_vars()`

, is a hidden way to send the survey object to the object (by hidden, I mean that the user doesn’t have to specify the survey in the arguments of their function call). To use it, you can now directly call`cur_svy()`

from inside your function. This survey includes only the current group’s survey data.`cur_svy_full()`

- Like`cur_svy()`

, but includes the full survey data intead of just the current group’s data.`cur_svy_wts()`

- This helper function provides access to the full-sample weights for the current group’s data.`set_survey_vars()`

- Many survey functions have limited support for both supplying a formula indicating the variables to calculate a statistic on as well as a vector. However, oftentimes the vector version is less well supported than the formula version. Since srvyr uses dplyr semantics, it ends up returning the values as vectors. This function will add on the variable to the survey, defaulting to having the name “__SRVYR_TEMP_VAR__”.`get_var_est()`

- A helper function that calculates variance estimates like standard error (se), confidence interval (ci), variance (var), or coefficient of variance (cv). For functions that support it, there is a separate argument for design effects (to match survey’s conventions).`as_srvyr_result_df()`

- A helper function that adds the`srvyr_result_df`

class to a`data.frame`

Note that these functions may not work in all cases. In srvyr, I’ve
actually had to write multiple versions of `get_var_est()`

because of minor differences in the way survey objects are returned.
Hopefully they will help in most situations, or at least give you a good
place to start.

Two less important conventions that srvyr functions follow are:

- snake_case function names (to better match the tidyverse)
- Multiple choice arguments that default to the first (so for var_type, if no parameters are specified, use only “se” not all of them).

That was just a lot of text, but I think it’s probably easiest just
to provide an example. The convey package provides several methods for
analysis of inequality using survey data. The svygini function
calculates the gini coefficient. Here, we’ll write functions that make a
srvyr version `survey_gini`

.

```
# S3 generic function
survey_gini <- function(
x, na.rm = FALSE, vartype = c("se", "ci", "var", "cv"), ...
) {
if (missing(vartype)) vartype <- "se"
vartype <- match.arg(vartype, several.ok = TRUE)
.svy <- srvyr::set_survey_vars(srvyr::cur_svy(), x)
out <- convey::svygini(~`__SRVYR_TEMP_VAR__`, na.rm = na.rm, design = .svy)
out <- srvyr::get_var_est(out, vartype)
as_srvyr_result_df(out)
}
```

And here’s what this function looks like in practice:

```
# Example from ?convey::svygini
suppressPackageStartupMessages({
library(srvyr)
library(survey)
library(convey)
library(laeken)
})
data(eusilc) ; names( eusilc ) <- tolower( names( eusilc ) )
# Setup for survey package
des_eusilc <- svydesign(
ids = ~rb030,
strata = ~db040,
weights = ~rb050,
data = eusilc
)
des_eusilc <- convey_prep(des_eusilc)
# Setup for srvyr package
srvyr_eusilc <- eusilc %>%
as_survey(
ids = rb030,
strata = db040,
weights = rb050
) %>%
convey_prep()
## Ungrouped
# Calculate ungrouped for survey package
svygini(~eqincome, design = des_eusilc)
#> gini SE
#> eqincome 0.26497 0.0019
# Use new function from summarize
srvyr_eusilc %>%
summarize(eqincome = survey_gini(eqincome))
#> # A tibble: 1 × 2
#> eqincome eqincome_se
#> <dbl> <dbl>
#> 1 0.265 0.00195
## Groups
# Calculate by groups for survey
survey::svyby(~eqincome, ~rb090, des_eusilc, convey::svygini)
#> rb090 eqincome se
#> male male 0.2578983 0.002617279
#> female female 0.2702080 0.002892713
# Use new function from summarize
srvyr_eusilc %>%
group_by(rb090) %>%
summarize(eqincome = survey_gini(eqincome))
#> # A tibble: 2 × 3
#> rb090 eqincome eqincome_se
#> <fct> <dbl> <dbl>
#> 1 male 0.258 0.00262
#> 2 female 0.270 0.00289
```