Add a contrast to a data frame

add_contrast(
  data,
  col,
  contrast = c("anova", "sum", "treatment", "helmert", "poly", "difference"),
  levels = NULL,
  ...,
  add_cols = TRUE,
  colnames = NULL
)

Arguments

data: the data frame
col: the column to recode
contrast: the contrast to recode to
levels: the levels of the factor in order
...: arguments to pass to the contrast function (base or omit)
add_cols: whether to just add the contrast to the existing column or also to create new explicit columns in the dataset (default)
colnames: optional list of column names for the added contrasts

Value

the data frame with the recoded column and added columns (if add_cols == TRUE)

Examples

df <- sim_design(between = list(time = 1:6), plot = FALSE) %>%
   add_contrast("time", "poly")

# test all polynomial contrasts
lm(y ~ time, df) %>% broom::tidy()
#> # A tibble: 6 × 5
#>   term        estimate std.error statistic p.value
#>   <chr>          <dbl>     <dbl>     <dbl>   <dbl>
#> 1 (Intercept)  -0.0328    0.0417    -0.786   0.432
#> 2 time^1        0.0370    0.102      0.362   0.718
#> 3 time^2       -0.0534    0.102     -0.522   0.602
#> 4 time^3        0.0928    0.102      0.909   0.364
#> 5 time^4       -0.0229    0.102     -0.224   0.823
#> 6 time^5       -0.0205    0.102     -0.201   0.841

# test only the linear and quadratic contrasts
lm(y ~ `time^1` + `time^2`, df) %>% broom::tidy()
#> # A tibble: 3 × 5
#>   term        estimate std.error statistic p.value
#>   <chr>          <dbl>     <dbl>     <dbl>   <dbl>
#> 1 (Intercept)  -0.0328    0.0416    -0.787   0.431
#> 2 `time^1`      0.0370    0.102      0.363   0.717
#> 3 `time^2`     -0.0534    0.102     -0.523   0.601