Author: Spencer Graves, Sundar Dorai-Raj, and Romain François
Date: 2024-06-28

# Searching help pages of R packages

#### Spencer Graves, Sundar Dorai-Raj, and Romain François

#### 2024-06-28

    library(sos)
    #> Loading required package: brew
    #>
    #> Attaching package: 'sos'
    #> The following object is masked from 'package:utils':
    #>
    #>     ?

This vignette was originally published in The R Journal, vol. 1(2) in 2009. The package and this vignette have been changed since then to make the package easier to use and to adjust to changes in the R ecosystem.

## Abstract

The `sos` package provides a means to quickly and flexibly search the help pages of contributed packages, finding functions and datasets in seconds or minutes that could not be found in hours or days by any other means we know. Its `findFn` function searches the search site `https://search.r-project.org` used by the `RSiteSearch` function but returns the matches in a `data.frame` of class `findFn`, which can be further manipulated by other `sos` functions to produce, for example, an Excel file that starts with a summary sheet that makes it relatively easy to prioritize alternative packages for further study. As such, it provides a very powerful way to do a literature search for functions and packages relevant to a particular topic of interest and could become virtually mandatory for authors of new packages or papers in publications such as The R Journal and the Journal of Statistical Software.

## Introduction

The `sos` package provides a means to quickly and flexibly search the help pages of contributed packages, finding functions and datasets in seconds or minutes that could not be found in hours or days by any other means we know.

The main capability of this package is the `findFn` function, which scans the function entries in the `RSiteSearch` database, created originally by Jonathan Baron,1. It returns the matches in a `data.frame` of class `findFn`. This database includes options to search the help pages of R packages contributed to CRAN (the Comprehensive R Archive Network) plus a few other publicly available packages, as well as selected mailing list archives—primarily R-help. The `findFn` function focuses only on the help pages in this database, ignoring the R-help archives. (CRAN grew from 1700 contributed packages and bundles on 2009-03-11 to 1954 on 2009-09-18, adding over 40 packages per day, an annual growth rate of 31 percent.)

The `print` method for objects of class `findFn` displays the results as two tables in the default web browser.

- The first is the table of individual help pages with links to those help pages, sorted by package. The key benefit of this is that they results are sorted by package, displaying first the results from the package with the most matches. This behavior differs from that of the `RSiteSearch` function in the `utils` package in more ways than the sort order. First, `findFn` returns the results in R as a `data.frame`, which can be further manipulated. Second, the ultimate display in a web browser is a table, unlike the list produced by `RSiteSearch`.
- The second table is a package summary.

Other `sos` functions provide summaries with one line for each package, support the union and intersection of `findFn` objects, and translate a `findFn` object into an Excel file with three sheets:

# PackageSum2, which provides an enhanced summary of the packages with matches,

# the findFn table itself, and

# (the call used to produce it.

Three examples are considered below:
* First we find a data set containing a variable `Petal.Length`}`. * Second, we study R capabilities for splines, including looking for a function named`spline`.
* Third, we search for contributed R packages with capabilities for solving differential equations.

## Finding a variable in a data set

Chambers (2009)2 uses a variable `Petal.Length` from a famous Fisher data set but without naming the data set nor indicating where it can be found nor even if it exists in any contributed R package. The sample code he provides does not work by itself. To get his code to work to produce his Figure 7.2, we must first obtain a copy of this famous data set in a format compatible with his code.

To look for this data set, one might first try the `help.search` function. Unfortunately, this function returns nothing in this case:

    (Petal.Length <- help.search('Petal.Length'))
    #> No vignettes or demos or help files found with alias or concept or
    #> title matching 'Petal.Length' using regular expression matching.

When this failed, many users might then try

    library(sos)
    if(!CRAN()){
      RSiteSearch('Petal.Length')
    }
    #> A search query has been submitted to https://search.r-project.org
    #> The results page should open in your browser shortly

This produced 80 matches when it was tried one day (and 62 matches a few months later).

`RSiteSearch('Petal.Length', 'function')` will identify only the help pages. We can get something similar and for many purposes more useful, as follows:

    library(sos)
    PL <- findFn('Petal.Length')
    #> found 200 matches;  retrieving 10 pages
    #> 2 3 4 5 6 7 8 9 10
    #>
    #> Downloaded 200 links in 129 packages.

    class(PL)
    #> [1] "findFn"     "data.frame"

    dim(PL)
    #> [1] 200  10

`PL` is a data frame of class `findFn` identifying all the help pages in the `RSiteSearch` database matching the search term (unless the number of matches exceeds the `20*maxPages` argument of `findFn`, assuming 20 links per page). An alias for `findFn` is `???`. Thus, this same search can be performed as follows:

    PL. <- ???Petal.Length
    #> found 200 matches;  retrieving 10 pages
    #> 2 3 4 5 6 7 8 9 10
    #>
    #> Downloaded 200 links in 129 packages.

    class(PL.)
    #> [1] "findFn"     "data.frame"

    dim(PL.)
    #> [1] 200  10

(The `???` alias only works in an assignment, so to print immediately, you need something like `(PL <- ???Petal.Length)`.)

The `data.frame`s `PL` and `PL.` should be identical unless the search site `https://search.r-project.org` changes in the time between these two searches.

Both `data.frame`s have columns `Count`, `MaxScore`, `TotalScore`, `Package`, `Function`, `Date`, `Score`, `Description`, and `Link`. `Function` is the name of the help page, not the name of the function for two reasons:

# Multiple functions may be documented on a single

help page. # Some help pages document other things such as data sets.

`Score` is the index of the strength of the match. It is used by the `RSiteSearch` database to decide which items to display first. `Package` is the name of the package containing `Function`. `Count` gives the total number of matches in `Package` found in this `findFn` call. By default, the `findFn` object is sorted by `Count`, `MaxScore`, `TotalScore`, and `Package` (to place the most important `Package` first), then by `Score`}`and`Function`.

The `summary` method for an object of class `FindFn` prints a table giving for each `Package` the `Count` (number of matches), `MaxScore` (max of `Score`), `TotalScore` (sum of `Score`), and `Date`, sorted like a Pareto chart to place the `Package` with the most help pages first:

    # the following table has been
    # manually edited for clarity
    summary(PL)

    #> $PackageSummary
    #>  Package Count MaxScore TotalScore Date pkgLink
    #>     <NA>  <NA>     <NA>       <NA> <NA>    <NA>
    #>    <...>
    #>     <NA>  <NA>     <NA>       <NA> <NA>    <NA>
    #>    <...>
    #>
    #> $minPackages
    #> [1] 12
    #>
    #> $minCount
    #> [1] 3
    #>
    #> $matches
    #> [1] 200
    #>
    #> $nrow
    #> [1] 200
    #>
    #> $nPackages
    #> [1] 129
    #>
    #> $string
    #> [1] "Petal.Length"
    #>
    #> $call
    #> findFn(string = "Petal.Length")
    #>
    #> attr(,"class")
    #> [1] "summary.findFn" "list"

(The `Date` here is the date that this package was added to the `RSiteSearch` database.)

One of the listed packages is `datasets`. Since it is part of the default R distribution, we decide to look there first. We can select that row of `PL` just like we would select a row from any other data frame:

    PL[PL$Package == 'datasets', 'Function']

    #> [1] "iris"

Problem solved in less than a minute! Any other method known to the present authors would have taken substantially more time.

## Finding packages with spline capabilities

In 2005, the lead author of this article decided he needed to learn more about splines. A literature search began as follows:

    if(!CRAN()){
      RSiteSearch('spline')
    }

(using the `RSiteSearch` function in the `utils` package). While preparing this manuscript, this command identified 1526 documents one day. That is too many. It can be restricted to functions as follows:

    if(!CRAN()){
      RSiteSearch('spline', 'fun')
    }

This identified only 739 one day (631 earlier). That’s an improvement over 739 but is still too many for convenient analysis. To get a quick overview of these matches, can proceed as follows:

    if(!CRAN()){
      RSiteSearch('spline', 'fun')
    }

This downloaded a summary of the highest-scoring help pages in the `RSiteSearch` data base in roughly 5-15 seconds, depending on the speeds of the database and Internet connection.

If the search results exceeds the `maxPages` argument, increase that argument from its default 100:

    splineAll <- findFn('spline', maxPages = 999)

If we want to find a function named `spline`, we can proceed as follows:

    selSpl <- splineAll[, 'Function'] == 'spline'
    splineAll[selSpl, ]

This has 0 rows, because there is no help page named `spline`. This does not mean that no function with that exact name exists, only that no help page has that name.

To look for help pages whose name includes the characters `spline`, we can use `grepFn`:

    if(!CRAN()){
      grepFn('spline', splineAll, ignore.case = TRUE)
    }

This returned a `findFn` object identifying 426 help pages. When this was run while preparing this manuscript, the sixth row was `lspline` in the `assist` package, which has a Score of 1. (On another day, the results could be different, because the `RSiteSearch` database changes over time.) This was the sixth row in this table, because it is in the `assist` package, which had a total of 34 help pages matching the search term, but this was the only one whose name matched the `pattern` passed to `grepFn`.

We could next `print` the `splineAll` `findFn` object. However, it may not be easy to digest a table with 739 rows (or however many rows it produces when you run it).

`summary(splineAll)` would tell us that the 5264 help pages came from 1222 different packages and display the first `minPackages = 12` such packages. (If other packages had the same number of matches as the twelfth package, they would also appear in this summary. `minPackages is an argument of the`summary.findFn` function and can be changed if the user wishes.)

A more complete view can be obtained in MS Excel format using the `writeFindFn2xls` function:

    writeFindFn2xls(splineAll)
    #> Loading required package: WriteXLS
    #> A system perl installation found in /opt/local/bin/perl
    #> The perl modules included with WriteXLS are located in /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/library/WriteXLS/Perl
    #> All required Perl modules were found.

(`findFn2xls` is an alias for `writeFindFn2xls`. We use the longer version here, as it may be easier to remember.)

If either the `WriteXLS` package and compatible Perl code are properly installed or if you are running Windows with the `RODBC` package, this produces an Excel file in the working directory named `splineAll.xls`, containing the following three worksheets:

- The PackageSum2 sheet includes one line for each package with a matching help page, enhanced by providing information for locally installed packages not available in the `findFn` object.
- The findFn sheet contains the search results.
- The call sheet gives the call to `findFn` that generated these search results.

If `writeFindFn2xls` cannot produce an Excel file with your installation, it will write three `csv`}`files with names`splineAll-sum.csv`}`, `splineAll.csv`, and `splineAll-call.csv`, corresponding to the three worksheets described above. (Users who do not have MS Excel may like to know that Open Office Calc can open a standard `xls`}` file and can similarly create such files.)3

The PackageSum2 sheet is created by the PackageSum2 function, which adds information from installed packages not obtained by `findFn`. The extended summary includes the package title and date, plus the names of the author and the maintainer, the number of help pages in the package, and the name(s) of any vignettes. This can be quite valuable in prioritizing packages for further study. Other things being equal, we think most people would rather learn how to use a package being actively maintained than one that has not changed in five years. Similarly, we might prefer to study a capability in a larger package than a smaller one, because the rest of the package might provide other useful tools or a broader context for understanding the capability of interest.

These extra fields, package title, etc., are blank for packages in the `findFn` object not installed locally. For installed packages, the `Date` refers to the packaged date rather than the date the package was added to the `RSiteSearch` database.

Therefore, the value of `PackageSum2` can be increased by running `install.packages` (from the `utils` package) to install packages not currently available locally and `update.packages` to ensure the local availability of the latest versions for all installed packages.

To make it easier to add desired packages, the `sos` package includes an `installPackages` function, which checks all the packages in a `findFn` object for which the number of matches exceeds a second argument `minCount` and installs any of those not already available locally; the default `minCount` is the square root of the largest `Count`. Therefore, the results from `PackageSum2` and the `PackageSum2` sheet created by `writeFindFn2xls` will typically contain more information after running `installPackages` than before.

To summarize, three lines of code gave us a very powerful summary of spline capabilities in contributed R packages:

    splineAll <- findFn('spline', maxPages = 999)
    # Do not include in auto test
    #installPackages(splineAll)
    writeFindFn2xls(splineAll)
    #> A system perl installation found in /opt/local/bin/perl
    #> The perl modules included with WriteXLS are located in /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/library/WriteXLS/Perl
    #> All required Perl modules were found.

The resulting `splineAll.xls` file can help establish priorities for further study of the different packages and functions. An analysis of this nature almost four years ago led the lead author to the `fda` package and its companion books, which further led to a collaboration that has produced joint presentations at three different conferences and a joint book.4

## Combining search results

The lead author of this article recently gave an invited presentation on “Fitting Nonlinear Differential Equations to Data in R”^[Workshop on Statistical Methods for Dynamic System Models, Vancouver, 2009: `http://stat.sfu.ca/~dac5/workshop09/Spencer_Graves.html`. A key part of preparing for that presentation was a search of contributed R code, which proceeded roughly as follows:

    de <- findFn('differential equation')
    des <- findFn('differential equations')
    de. <- de | des

When this was run in 2009, the object `de` had 53 rows, while `des` had 105. If this search engine were simply searching for character strings, `de` would be larger than `des`; in this case, it was smaller. The last object `de.` is the union of `de` and `des`; | is an alias for `unionFindFn`. In 2009 the `de.` object had 124 rows. That suggests that the corresponding intersection must have had (53+105-124) = 34 rows. This can be confirmed via `nrow(de \& des)`. (& is an alias for `intersectFindFn`.)

To make everything in `de.` locally available, we can use `installPackages(de., minCount = 1)`. This installed all referenced packages except `rmutil` and a dependency `Biobase`, which were not available on CRAN but are included in the `RSiteSearch` database.

Next, `writeFindFn2xls(de.)` produced a file `de..xls` in the working directory. [(]The working directory can be identified via `getwd()`.]

The `PackageSum2` sheet of that Excel file provided a quick summary of packages with matches, sorted to put the package with the most matches first. In this case, this first package was `deSolve`, which provides, “General solvers for initial value problems of ordinary differential equations (ODE), partial differential equations (PDE) and differential algebraic equations (DAE)”. This is clearly quite relevant to the subject. The second package was `PKfit`, which is “A Data Analysis Tool for Pharmacokinetics”. This may be too specialized for general use. I therefore would not want to study this first unless my primary interest here was in pharmacokinetic models.

By studying the summary page in this way, I was able to decide relatively quickly which packages I should consider first. In making this decision, I gave more weight to packages with one or more vignettes and less weight to those where the `Date` was old, indicating that the code was not being actively maintained and updated. I also checked the conference information to make sure I did not embarrass myself by overlooking a package authored or maintained by another invited speaker.

## Discussion

We have found `findFn` in the `sos` package to be very quick, efficient and effective for finding things in contributed packages. The `grepFn` function helps quickly look for functions (or help pages) with particular names. The capabilities in `unionFindFn` and `intersectFindFn` (especially via their **|*} and &** aliases) can be quite useful where a single search term seems inadequate; they make it easy to combine multiple searches to produce something closer to what is desired. An example of this was provided with searching for both `differential equation'' and`differential equations’’.

The PackageSum2 sheet of an Excel file produced by `writeFindFn2xls` (after also running the `installPackages` function) is quite valuable for understanding the general capabilities available for a particular topic. This could be of great value for authors to find what is already available so they don’t duplicate something that already exists and so their new contributions appropriately consider the contents of other packages.

The `findFn` capability can also reduce the risk of “the researcher’s nightmare” of being told after substantial work that someone else has already done it.

## Acknowledgments

The capabilities described here extend the power of the R Site Search search engine originally maintained by Jonathan Baron. Without Prof. Baron’s support, it would not have been feasible to develop the features described here. Duncan Murdoch, Marc Schwarz, Dirk Eddelbuettel, Gabor Grothendiek and anonymous referees contributed suggestions for improvement, but of course can not be blamed for any deficiencies. The collaboration required to produce the current `sos` package was greatly facilitated by R-Forge5. The `sos` package is part of the R Site Search project hosted there. This project also includes code for a Firefox extension to simplify the process of finding information about R from within Firefox. This Firefox extension is still being developed with the current version downloadable from `http://addictedtor.free.fr/rsitesearch`.

Spencer Graves EffectiveDefense.org Kansas City, Missouri email spencer.graves@effectivedefense.org

Sundar Dorai-Raj Google Mountain View, CA email sdorairaj@google.com

Romain François Independent R Consultant Montpellier, France email francoisromain@free.fr

1. @JB09URL↩︎

2. @JC09↩︎

3. @CALC09MAN↩︎

4. @RHG09↩︎

5. @RFORGE09URL↩︎