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Frequently Asked Questions (FAQ)

Source: vignettes/faq.Rmd
faq.Rmd

Quick answers to common questions about RandomWalker.

General Questions

What is RandomWalker?

RandomWalker is an R package for generating, visualizing, and analyzing random walks. It supports 27+ probability distributions, multi-dimensional walks (1D, 2D, 3D), and provides tidyverse-compatible functions for data manipulation and analysis.

Who should use RandomWalker?

RandomWalker is useful for: - Researchers: Modeling stochastic processes, simulating experiments - Students: Learning probability and statistics - Data Scientists: Generating synthetic data, testing algorithms - Financial Analysts: Modeling asset prices, risk analysis - Physicists/Biologists: Simulating particle movement, organism behavior - Educators: Teaching probability concepts

Is RandomWalker free to use?

Yes! RandomWalker is open-source software licensed under the MIT License. You can use it freely for academic, commercial, or personal projects.

Installation Questions

How do I install RandomWalker? 

# From CRAN (stable)
install.packages("RandomWalker")

# From GitHub (development)
devtools::install_github("spsanderson/RandomWalker")

What R version do I need?

RandomWalker requires R version 4.1.0 or higher.

Why am I getting dependency errors?

Try installing dependencies manually:

install.packages(c("dplyr", "tidyr", "purrr", "rlang", "patchwork", "NNS", "ggiraph"))

Usage Questions

How do I generate a simple random walk? 

library(RandomWalker)
rw30() |> head(10)  # Generates 30 walks with 100 steps each
#> # A tibble: 10 × 3
#>    walk_number step_number     y
#>    <fct>             <int> <dbl>
#>  1 1                     1  0   
#>  2 1                     2 -1.40
#>  3 1                     3 -1.14
#>  4 1                     4 -3.58
#>  5 1                     5 -3.59
#>  6 1                     6 -2.97
#>  7 1                     7 -1.82
#>  8 1                     8 -3.64
#>  9 1                     9 -3.89
#> 10 1                    10 -4.13

How do I visualize my random walks?

Visualization of random walks showing multiple panels

How do I create a custom random walk?

Use one of the generator functions:

random_normal_walk(
  .num_walks = 10,
  .n = 100,
  .mu = 0,
  .sd = 1,
  .initial_value = 0
) |> visualize_walks()

Custom normal random walk with specified parameters

Can I set a seed for reproducibility?

Yes:

set.seed(123)
walks <- rw30()

# Same seed produces same result
set.seed(123)
walks2 <- rw30()
identical(walks, walks2)  # TRUE
#> [1] TRUE

Distribution Questions

Which distribution should I use?

It depends on your use case:

What’s the difference between random_normal_walk() and brownian_motion()?

Both use normal distributions, but: - random_normal_walk(): Discrete steps, cumulative sum - brownian_motion(): Continuous-time stochastic process, includes drift (μ) and volatility (σ) parameters

For most purposes, they’re similar. Use brownian_motion() for financial modeling.

What’s the difference between brownian_motion() and geometric_brownian_motion()?

  • Brownian Motion: Can go negative, additive process

    X(t) = X(0) + μt + σW(t)

  • Geometric Brownian Motion: Always positive, multiplicative process

    X(t) = X(0) exp((μ - σ²/2)t + σW(t))

Use Geometric Brownian Motion for modeling stock prices (can’t go negative).

Can I use custom distributions?

Yes! Use custom_walk():

# Custom displacement function
my_displacement <- function() {
  # Your custom logic here
  return(some_value)
}

custom_walk(
  .num_walks = 10,
  .n = 100,
  .custom_fns = my_displacement
)

Multi-Dimensional Questions

How do I create a 2D random walk?

Add .dimensions = 2:

random_normal_walk(.num_walks = 10, .n = 100, .dimensions = 2)
#> # A tibble: 800 × 14
#>    walk_number step_number        x        y cum_sum_x cum_sum_y cum_prod_x
#>    <fct>             <int>    <dbl>    <dbl>     <dbl>     <dbl>      <dbl>
#>  1 1                     1 -0.220   -0.119      -0.220   -0.119           0
#>  2 1                     2 -0.0624   0.0535     -0.283   -0.0658          0
#>  3 1                     3 -0.220    0.179      -0.503    0.113           0
#>  4 1                     4  0.146    0.0317     -0.357    0.145           0
#>  5 1                     5 -0.0783  -0.0700     -0.435    0.0749          0
#>  6 1                     6 -0.147   -0.00606    -0.582    0.0689          0
#>  7 1                     7 -0.00374 -0.0842     -0.586   -0.0154          0
#>  8 1                     8  0.170   -0.115      -0.416   -0.130           0
#>  9 1                     9 -0.0349   0.0425     -0.451   -0.0880          0
#> 10 1                    10 -0.0472  -0.119      -0.498   -0.207           0
#> # ℹ 790 more rows
#> # ℹ 7 more variables: cum_prod_y <dbl>, cum_min_x <dbl>, cum_min_y <dbl>,
#> #   cum_max_x <dbl>, cum_max_y <dbl>, cum_mean_x <dbl>, cum_mean_y <dbl>

How do I visualize 2D walks? 

library(ggplot2)

walk_2d <- random_normal_walk(.num_walks = 10, .n = 100, .dimensions = 2)

ggplot(walk_2d, aes(x = cum_sum_x, y = cum_sum_y, color = walk_number)) +
  geom_path() +
  coord_equal() +
  theme_minimal()

2D random walk visualization with x-y coordinates

What’s the difference between x, y in 1D vs 2D walks?

  • 1D: y is the random value, x is renamed to step_number
  • 2D: x and y are the two spatial dimensions
  • 3D: x, y, and z are the three spatial dimensions

Visualization Questions

How do I make interactive plots?

Add .interactive = TRUE:

rw30() |> visualize_walks(.interactive = TRUE)

How do I show only specific panels?

Use .pluck:

# Single panel
random_normal_walk() |> visualize_walks(.pluck = "cum_sum")

Single panel visualization showing cumulative sum

# Multiple panels
random_normal_walk() |> visualize_walks(.pluck = c("y", "cum_sum", "cum_mean"))

Multiple panel visualization showing y, cumulative sum, and cumulative mean

How do I adjust transparency?

Use .alpha:

rw30() |> visualize_walks(.alpha = 0.3)  # More transparent
rw30() |> visualize_walks(.alpha = 0.9)  # More opaque

How do I export plots? 

library(ggplot2)

p <- rw30() |> visualize_walks()
ggsave("my_plot.png", p, width = 12, height = 8, dpi = 300)

Can I customize colors?

Yes, using ggplot2:

p <- random_normal_walk(.num_walks = 5) |>
  visualize_walks(.pluck = "y")

p + scale_color_viridis_d()

Random walk with custom color palette

Statistical Analysis Questions

How do I get summary statistics? 

walks <- rw30()

# Overall summary
walks |> summarize_walks(.value = y)
#> Registered S3 method overwritten by 'quantmod':
#>   method            from
#>   as.zoo.data.frame zoo
#> Warning: There was 1 warning in `dplyr::summarize()`.
#> ℹ In argument: `geometric_mean = exp(mean(log(y)))`.
#> Caused by warning in `log()`:
#> ! NaNs produced
#> # A tibble: 1 × 16
#>   fns   fns_name dimensions mean_val median range quantile_lo quantile_hi
#>   <chr> <chr>         <dbl>    <dbl>  <dbl> <dbl>       <dbl>       <dbl>
#> 1 rw30  Rw30              1    -1.09  -1.02  46.9       -12.6        11.5
#> # ℹ 8 more variables: variance <dbl>, sd <dbl>, min_val <dbl>, max_val <dbl>,
#> #   harmonic_mean <dbl>, geometric_mean <dbl>, skewness <dbl>, kurtosis <dbl>
# By walk
walks |> summarize_walks(.value = y, .group_var = walk_number) |> head()
#> Warning: There were 29 warnings in `dplyr::summarize()`.
#> The first warning was:
#> ℹ In argument: `geometric_mean = exp(mean(log(y)))`.
#> ℹ In group 1: `walk_number = 1`.
#> Caused by warning in `log()`:
#> ! NaNs produced
#> ℹ Run `dplyr::last_dplyr_warnings()` to see the 28 remaining warnings.
#> # A tibble: 6 × 17
#>   walk_number fns   fns_name dimensions mean_val median range quantile_lo
#>   <fct>       <chr> <chr>         <dbl>    <dbl>  <dbl> <dbl>       <dbl>
#> 1 1           rw30  Rw30              1     5.98   7.45 20.1        -3.74
#> 2 2           rw30  Rw30              1    -4.14  -4.44  9.07       -7.77
#> 3 3           rw30  Rw30              1    -6.56  -6.94 11.7       -10.9 
#> 4 4           rw30  Rw30              1    -1.04  -1.05  6.63       -3.40
#> 5 5           rw30  Rw30              1     2.89   2.22 17.4        -3.46
#> 6 6           rw30  Rw30              1    -4.08  -4.59 14.0        -9.72
#> # ℹ 9 more variables: quantile_hi <dbl>, variance <dbl>, sd <dbl>,
#> #   min_val <dbl>, max_val <dbl>, harmonic_mean <dbl>, geometric_mean <dbl>,
#> #   skewness <dbl>, kurtosis <dbl>

What statistics are included?

  • Mean, median, range
  • Variance, standard deviation
  • Quantiles (2.5% and 97.5% by default)
  • Min, max
  • Harmonic mean, geometric mean
  • Skewness, kurtosis

How do I subset walks by extremes? 

walks <- rw30()

# Get walk with maximum final value
max_walk <- walks |> subset_walks(.value = "y", .type = "max")

# Get walk with minimum final value
min_walk <- walks |> subset_walks(.value = "y", .type = "min")

# Visualize both walks together
combined <- dplyr::bind_rows(
  dplyr::mutate(max_walk, type = "Maximum"),
  dplyr::mutate(min_walk, type = "Minimum")
)
visualize_walks(combined, .pluck = "y") +
  ggplot2::facet_wrap(~type)

Maximum and minimum walks visualization

Performance Questions

How many walks can I generate?

This depends on your system, but RandomWalker can handle: - Light: 1,000 walks × 1,000 steps each - Moderate: 10,000 walks × 10,000 steps each - Heavy: 100,000+ walks with careful memory management

My visualization is slow. How do I speed it up?

  1. Reduce transparency: .alpha = 0.2
  2. Sample walks: Show fewer walks
  3. Downsample steps: Keep every nth step
  4. Use static plots: Disable .interactive 
# Sample walks
walks_large |>
  filter(walk_number %in% sample(levels(walk_number), 50)) |>
  visualize_walks(.alpha = 0.2)

# Downsample steps
walks_large |>
  filter(step_number %% 10 == 0) |>
  visualize_walks()

Can I parallelize generation?

The functions are vectorized, but you can use parallel processing:

library(future)
library(furrr)

plan(multisession, workers = 4)

walks_list <- future_map(1:10, ~random_normal_walk(.num_walks = 100), .options = furrr_options(seed = 123))

Data Structure Questions

What format does RandomWalker return?

A tibble (tidyverse-compatible data frame) with columns: - walk_number (factor) - step_number (integer) - Value columns (y for 1D, x/y for 2D, x/y/z for 3D) - Cumulative function columns

How do I access attributes? 

walks <- rw30()
atb <- get_attributes(walks)
names(atb)
#> [1] "names"     "class"     "num_walks" "num_steps" "mu"        "sd"       
#> [7] "fns"       "dimension"

Common attributes: fns, num_walks, n, initial_value, distribution parameters.

Can I convert to other formats?

Yes:

# To base R data.frame
as.data.frame(walks)

# To matrix (values only)
walks |> select(y) |> as.matrix()

# To time series
ts(walks$y, frequency = 1)

# To wide format
walks |> tidyr::pivot_wider(names_from = walk_number, values_from = y)

Error Messages

“The value to summarize must be provided”

You forgot to specify .value in summarize_walks():

# Wrong
walks |> summarize_walks()

# Correct
walks |> summarize_walks(.value = y)

“object ‘y’ not found”

You might be using a 2D/3D walk where y refers to a dimension. Use cum_sum_y or specify dimensions:

walk_2d <- random_normal_walk(.dimensions = 2)

# Wrong
walk_2d |> summarize_walks(.value = y)

# Correct
walk_2d |> summarize_walks(.value = cum_sum_y)

Integration Questions

Does RandomWalker work with dplyr?

Yes! RandomWalker is designed for tidyverse:

library(dplyr)

random_normal_walk(.num_walks = 10) |>
  filter(step_number > 50) |>
  mutate(positive = cum_sum_y > 0) |>
  group_by(walk_number) |>
  summarize(prop_positive = mean(positive))
#> # A tibble: 10 × 2
#>    walk_number prop_positive
#>    <fct>               <dbl>
#>  1 1                     0.9
#>  2 2                     1  
#>  3 3                     1  
#>  4 4                     1  
#>  5 5                     1  
#>  6 6                     0  
#>  7 7                     1  
#>  8 8                     0  
#>  9 9                     1  
#> 10 10                    0.1

Can I use it in Shiny apps?

Yes:

library(shiny)
library(RandomWalker)

ui <- fluidPage(
  numericInput("num_walks", "Number of Walks:", 10),
  plotOutput("walks_plot")
)

server <- function(input, output) {
  output$walks_plot <- renderPlot({
    random_normal_walk(.num_walks = input$num_walks) |>
      visualize_walks(.pluck = "cum_sum")
  })
}

shinyApp(ui, server)

Can I use it with ggplot2?

Yes, visualize_walks() returns ggplot2 objects:

library(ggplot2)

p <- rw30() |> visualize_walks(.pluck = "y")

# Customize further
p +
  labs(title = "My Custom Title") +
  theme_bw()

Custom ggplot2 theme applied to random walk

Application Questions

How do I model stock prices?

Use Geometric Brownian Motion:

stock_prices <- geometric_brownian_motion(
  .num_walks = 100,
  .n = 252,  # Trading days
  .mu = 0.08,  # 8% expected return
  .sigma = 0.25,  # 25% volatility
  .initial_value = 100
)
visualize_walks(stock_prices)

Stock price simulation using geometric Brownian motion

How do I simulate particle diffusion?

Use Brownian Motion in 2D or 3D:

particles <- brownian_motion(
  .num_walks = 50,
  .n = 1000,
  .dimensions = 3
)

How do I test an algorithm?

Generate synthetic data:

# Generate test walks
test_data <- discrete_walk(
  .num_walks = 1000,
  .n = 100,
  .upper_probability = 0.5
)

# Run your algorithm
result <- my_algorithm(test_data)

Getting Help

Where can I find more examples?

  • Getting Started Vignette - Basic examples
  • Package Documentation - Function reference
  • GitHub Repository - Real-world applications

Where do I report bugs?

GitHub Issues

Where can I ask questions?

How do I cite RandomWalker? 

citation("RandomWalker")

Is there a community?

Yes! Join us on: - GitHub Discussions - Follow @spsanderson on Twitter

Contributing

Can I contribute?

Yes! We welcome contributions: - Bug reports - Feature requests - Code contributions - Documentation improvements - Examples and tutorials

How do I suggest a new feature?

Open an issue on GitHub Issues with: - Clear description of the feature - Use cases - Example code (if applicable)

What’s the difference between RandomWalker and other R packages?

RandomWalker is unique in: - Tidyverse compatibility - 27+ distributions in one package - Multi-dimensional support (1D/2D/3D) - Rich visualization capabilities - Comprehensive statistical analysis tools - Consistent API across all functions

Can RandomWalker handle big data?

Yes, but: - Use efficient data structures (tibbles) - Sample or downsample for visualization - Consider parallel processing for generation - Use appropriate hardware

Is RandomWalker actively maintained?

Yes! The package is actively developed with: - Regular updates - Bug fixes - New features - Community support

Check NEWS.md for latest updates.

Didn’t find your answer? Ask on GitHub Discussions!