---
title: "Introduction to the ScottKnott Package"
author: "Faria, J. C., Jelihovschi, E. G., Allaman, I. B."
date: "`r Sys.Date()`"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Introduction to the ScottKnott Package}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = '#>',
  fig.width = 6,
  fig.height = 4,
  fig.align = 'center'
)
```

## Overview

The **ScottKnott** package implements the Scott & Knott (1974) clustering
algorithm as a multiple comparison method in the context of Analysis of Variance
(ANOVA). Unlike classic procedures such as Tukey, Duncan, and Newman-Keuls, the
Scott & Knott method forms **non-overlapping groups** of treatment means: each
mean belongs to exactly one group, eliminating the ambiguity that arises when
groups share members.

The algorithm proceeds by sorting the observed treatment means in decreasing
order and then recursively partitioning them into two sub-groups, applying a
likelihood-ratio test at each split. The process stops when no further
significant partition is found. The result is a complete, disjoint labelling of
the treatment means that is easy to interpret regardless of the number of
treatments.

```{r library}
library(ScottKnott)
```

---

## 1. Quick Start - Completely Randomized Design (CRD)

`CRD1` contains simulated data for a balanced CRD with **4 treatment levels**
and **6 replicates** per treatment. The main function `SK()` accepts a model
formula, an `aov` object, or an `lm` object. The `which` argument names the
factor to be compared.

```{r crd-quick}
data(CRD1)

sk1 <- with(CRD1,
            SK(y ~ x,
               data = dfm,
               which = 'x'))
summary(sk1)
```

The summary shows, for each level, the mean and the group letter assigned by the
algorithm. Levels sharing the same letter do not differ significantly at the
default 5 % level.

A single call to `plot()` produces the canonical dot plot with group letters
displayed above each point:

```{r crd-plot, fig.cap="CRD1: treatment means with min-max dispersion bars and SK groups."}
plot(sk1,
     dispersion = 'mm',
     d.col = 'steelblue')
```

---

## 2. Accepted Input Classes

`SK()` dispatches on the class of its first argument. The same grouping can be
obtained from a `formula`, an `aov` object, or an `lm` object.

```{r input-classes}
## From: aov
av1 <- with(CRD1, aov(y ~ x, data = dfm))
sk2 <- SK(av1, which = 'x')
summary(sk2)

## From: lm
lm1 <- with(CRD1, lm(y ~ x, data = dfm))
sk3 <- SK(lm1, which = 'x')
summary(sk3)
```

---

## 3. Unbalanced Data

When observations are missing, `SK()` automatically adjusts the means using the
Least-Squares Means methodology (via the **emmeans** package). The analysis
proceeds identically to the balanced case.

```{r crd-unbalanced}
## Remove the first observation to create an unbalanced dataset
u_sk1 <- with(CRD1,
              SK(y ~ x,
                 data = dfm[-1, ],
                 which = 'x'))
summary(u_sk1)
```

The number of replicates shown at the bottom of the plot reflects the actual
(unequal) sample sizes:

```{r plot-unbal, fig.cap="CRD1 (unbalanced): adjusted means with SD bars."}
plot(u_sk1, dispersion = 'sd', d.col = 'tomato')
```

---

## 4. Randomized Complete Block Design (RCBD)

`RCBD` contains simulated data for a design with **5 treatment levels** and **4
blocks**. The blocking factor `blk` is included in the formula; `which` selects
the factor of interest for the comparison.

```{r rcbd}
data(RCBD)

sk4 <- with(RCBD,
            SK(y ~ blk + tra,
               data = dfm,
               which = 'tra'))
summary(sk4)
```

```{r rcbd-plot, fig.cap="RCBD: treatment means with CI bars."}
plot(sk4,
     dispersion = 'ci',
     d.col = 'darkgreen',
     d.lty = 2)
```

---

## 5. Significance Level

The default significance level is `sig.level = 0.05`. Stricter or looser levels
lead to fewer or more groups, respectively.

```{r sig-level}
## alpha = 0.01 (stricter)
sk_01 <- with(RCBD,
              SK(y ~ blk + tra,
                 data = dfm,
                 which = 'tra',
                 sig.level = 0.01))

## alpha = 0.10 (looser)
sk_10 <- with(RCBD,
              SK(y ~ blk + tra,
                 data = dfm,
                 which = 'tra',
                 sig.level = 0.10))

cat('--- sig.level = 0.01 ---\n')
summary(sk_01)

cat('--- sig.level = 0.10 ---\n')
summary(sk_10)
```

---

## 6. Factorial Experiment (FE)

`FE` contains simulated data for a **3-factor factorial** design (N, P, K),
each at 2 levels, in 4 blocks. `SK()` supports both main-effect and nested
comparisons using colon notation in `which` and the `fl1` / `fl2` arguments to
select the level of the nesting factor.

```{r fe-main}
data(FE)

## Main effect: factor N
sk5 <- with(FE,
            SK(y ~ blk + N*P*K,
               data = dfm,
               which = 'N'))
summary(sk5)
```

```{r fe-nested}
## Nested: levels of N within level 1 of P
sk6 <- with(FE,
            SK(y ~ blk + N*P*K,
               data = dfm,
               which = 'P:N',
               fl1 = 1))
summary(sk6)

## Nested: levels of N within level 2 of P
sk7 <- with(FE,
            SK(y ~ blk + N*P*K,
               data = dfm,
               which = 'P:N',
               fl1 = 2))
summary(sk7)
```

---

## 7. Split-Plot Experiment (SPE)

`SPE` contains simulated data for a design with **3 whole plots** (factor P) and
**4 sub-plot treatments** (factor SP). When testing the whole-plot factor, the
appropriate error term must be specified via the `error` argument.

```{r spe}
data(SPE)

## Sub-plot factor SP (residual error, default)
sk8 <- with(SPE,
            SK(y ~ blk + P*SP + Error(blk/P),
               data = dfm,
               which = 'SP'))
summary(sk8)

## Whole-plot factor P (must specify the blk:P error term)
sk9 <- with(SPE,
            SK(y ~ blk + P*SP + Error(blk/P),
               data = dfm,
               which = 'P',
               error = 'blk:P'))
summary(sk9)
```

---

## 8. Visualisation Options

### 8.1 Dispersion bars

Four dispersion options are available for `plot.SK()`:

| Option  | Description                                |
|---------|--------------------------------------------|
| `'mm'`  | Min-max range (default)                    |
| `'sd'`  | ± 1 standard deviation                    |
| `'ci'`  | Individual 95 % confidence interval        |
| `'cip'` | Pooled 95 % confidence interval (uses MSE) |

`CRD2` provides a more visually rich example with **45 treatment levels**:

```{r plot-crd2, fig.width=8, fig.height=5, fig.cap="CRD2: 45 treatment means with pooled CI bars."}
data(CRD2)

sk10 <- with(CRD2,
             SK(y ~ x,
                data = dfm,
                which = 'x'))

plot(sk10,
     id.las = 2,
     yl = FALSE,
     dispersion = 'cip',
     d.col = 'steelblue')
```

### 8.2 Comparing all four options

```{r plot-four, fig.width=8, fig.height=7, fig.cap="The four dispersion options applied to CRD1. (A) mm: min-max range; (B) sd: standard deviation; (C) ci: individual confidence interval; (D) cip: pooled confidence interval."}
op <- par(mfrow = c(2, 2), mar = c(4, 3, 4, 1))

plot(sk1, dispersion = 'mm',  d.col = 'steelblue')
mtext('(A)', side = 3, adj = 0, line = 2, font = 2)

plot(sk1, dispersion = 'sd',  d.col = 'tomato')
mtext('(B)', side = 3, adj = 0, line = 2, font = 2)

plot(sk1, dispersion = 'ci',  d.col = 'darkgreen')
mtext('(C)', side = 3, adj = 0, line = 2, font = 2)

plot(sk1, dispersion = 'cip', d.col = 'purple')
mtext('(D)', side = 3, adj = 0, line = 2, font = 2)

par(op)
```

### 8.3 Boxplot

`boxplot.SK()` extends the standard boxplot by overlaying the SK group letters
above the frame and drawing the treatment mean inside each box.

```{r boxplot, fig.cap="CRD1: boxplot with SK group labels and means (red line)."}
## boxplot.SK re-evaluates the data argument from the original call;
## pass CRD1$dfm directly so it is findable in any environment.
sk1_bp <- SK(y ~ x,
             data = CRD1$dfm,
             which = 'x')

boxplot(sk1_bp,
        mean.col = 'red',
        mean.lwd = 2,
        args.legend = list(x = 'topright'))
```

---

## 9. Tabular Output

`xtable()` converts an `SK` result to an `xtable` object for inclusion in LaTeX
or HTML documents.

```{r xtable, results='asis'}
library(xtable)

tb <- xtable(sk4,
             caption = 'RCBD: Scott & Knott grouping of treatment means.',
             digits = 3)
print(tb,
      type = 'html',
      html.table.attributes = 'border="1" style="border-collapse:collapse; padding:4px;"',
      caption.placement = 'top',
      include.rownames = FALSE)
```

---

## 10. Mixed Models with lme4

`SK()` also accepts `lmerMod` objects from the **lme4** package, useful when
random effects need to be modelled explicitly.

```{r lmer, eval=requireNamespace('lme4', quietly=TRUE)}
library(lme4)

data(RCBD)

lmer1 <- with(RCBD,
              lmer(y ~ (1|blk) + tra,
                   data = dfm))

sk11 <- SK(lmer1, which = 'tra')
summary(sk11)
```

---

## References

Scott, R. J. and Knott, M. (1974). A cluster analysis method for grouping means
in the analysis of variance. *Biometrics*, **30**, 507-512.

Jelihovschi, E. G., Faria, J. C., and Allaman, I. B. (2014). ScottKnott: A
package for performing the Scott-Knott clustering algorithm in R. *Trends in
Applied and Computational Mathematics*, **15**(1), 3-17.

Conrado, T. V., Ferreira, D. F., Scapim, C. A., and Maluf, W. R. (2017).
Adjusting the Scott-Knott cluster analyses for unbalanced designs. *Crop
Breeding and Applied Biotechnology*, **17**(1), 1-9.
doi:10.1590/1984-70332017v17n1a1
