make_extract_features: Make feature extractor
In andybega/demspaces: Functions for the Democratic Spaces Project

Creates a feature extractor function

1	make_extract_features(x, n_comp = 5)

`x`	a `base::data.frame()` or similar object with only feature variables
`n_comp`	the number of components to keep

library("dplyr")
library("stats")
data("states")

# assume that the input consists entirely of features, and no NAs
train_x <- states %>%
  filter(year < 2010) %>%
  select(-starts_with("dv_"), -gwcode, -year) %>%
  filter(complete.cases(.))

test_x <- states %>%
  filter(year > 2009) %>%
  select(-starts_with("dv_"), -gwcode, -year) %>%
  filter(complete.cases(.))

featx <- make_extract_features(train_x)
featx(train_x)