The evaluation of `condition` resulted in an `NA`.  The `if` conditional must have either a `TRUE` or `FALSE` result.  

    if (NA) {}
    ## Error in if (NA) { : missing value where TRUE/FALSE needed

This can happen accidentally as the results of calculations:

    if(TRUE &amp;&amp; sqrt(-1)) {}
    ## Error in if (TRUE &amp;&amp; sqrt(-1)) { : missing value where TRUE/FALSE needed

----------


To test whether an object is missing use [`is.na(x)`][1] rather than `x == NA`.


----------


See also the related errors:

https://stackoverflow.com/q/12307139/134830

https://stackoverflow.com/q/27659841/134830

    if (NULL) {}
    ## Error in if (NULL) { : argument is of length zero
    
    if (&quot;not logical&quot;) {}
    ## Error: argument is not interpretable as logical
    
    if (c(TRUE, FALSE)) {}
    ## Warning message:
    ## the condition has length &gt; 1 and only the first element will be used


  [1]: http://www.inside-r.org/r-doc/base/is.na

I ran into this when checking on a null or empty string

    if (x == NULL || x == &#39;&#39;) {

changed it to

    if (is.null(x) || x == &#39;&#39;) {

  this works with `&quot;NA&quot;` not for `NA`
 

    comments = c(&quot;no&quot;,&quot;yes&quot;,&quot;NA&quot;)
      for (l in 1:length(comments)) {
        #if (!is.na(comments[l])) print(comments[l])
        if (comments[l] != &quot;NA&quot;) print(comments[l])
      }

I was getting this same error in my `forloops` with complex `if` statements. I fixed this issue by just wrapping my condition with `isTRUE`.

```
if(isTRUE(condition)==TRUE) {do something}
```

How can I centre the input field&#39;s placeholder&#39;s alignment in a html form?

I am using the following code, but it doesn&#39;t work:

CSS -&gt;

    input.placeholder {
    	text-align: center;
    }
    .emailField {
    	top:413px;
    	right:290px;
    	width: 355px;
    	height: 30px;
    	position: absolute;
    	border: none;
    	font-size: 17;
    	text-align: center;
    }

HTML -&gt;

    &lt;form action=&quot;&quot; method=&quot;POST&quot;&gt;
    	&lt;input type=&quot;text&quot; class=&quot;emailField&quot; placeholder=&quot;support@socialpic.org&quot; style=&quot;text-align: center&quot; name=&quot;email&quot; /&gt;
    	&lt;!&lt;input type=&quot;submit&quot; value=&quot;submit&quot; /&gt;  
    &lt;/form&gt;

Center HTML Input Text Field Placeholder

How can i split my long string constant over multiple lines?

I realize that you can do this:

    echo &quot;continuation \
    lines&quot;
    &gt;continuation lines

However, if you have indented code, it doesn&#39;t work out so well:

        echo &quot;continuation \
        lines&quot;
    &gt;continuation     lines


How to split strings over multiple lines in Bash?

I received this error message:

    Error in if (condition) { : missing value where TRUE/FALSE needed

or

    Error in while (condition) { : missing value where TRUE/FALSE needed

What does it mean, and how do I prevent it?



Error in if/while (condition) {: missing Value where TRUE/FALSE needed

I received this error message:
<pre><code class="hljs language-sql">Error in if (condition) { : missing value where TRUE/FALSE needed
</code></pre>
or
<pre><code class="hljs language-vbnet">Error in while (condition) { : missing value where TRUE/FALSE needed
</code></pre>
What does it mean, and how do I prevent it?

I&#39;ve seen some discussions in SO and other places regarding how this should be or will be done in future versions of Roxygen2. However, I am stuck. How should I go about documenting a S4 generic, as well as its methods, using Roxygen2? A working example for a brand new generic/methods, as well as an example for extending base S4 generic would be incredibly useful. I do not want to have to make separate (mostly) redundant documentation for each S4 method of the same generic. 

Due dilligence:
I have tracked down a useful example for the &quot;extract&quot; method. However, it appears to be outdated and incomplete for my question. It uses @slot tag in the class documentation, which is not (no longer?) supported. It only shows an extension of a core S4 method &quot;[&quot;, rather than a complete Roxygen example including the documentation of the S4 generic. 

https://stackoverflow.com/questions/4396768/how-to-properly-document-s4-and-methods-using-roxygen

If I fully document a new S4 generic with title, description `@param @return @name @aliases 
@docType @rdname`, and then document the S4 method with just the corresponding `@name @aliases 
@docType @rdname`, I get the following `R CMD check` warning:

    * checking for missing documentation entries ... WARNING
    Undocumented S4 methods:
    &lt;&lt; long list of apparently undocumented methods. E.g. generic &#39;plot&#39; and siglist &#39;myClass1,ANY&#39; &gt;&gt;
    All user-level objects in a package (including S4 classes and methods)
    should have documentation entries.

It looked at first as though none of my S4 methods documented in this fashion with roxygen2 had actually worked. However, so far, I&#39;ve noticed that my extensions of the core method &quot;show&quot; do not have an associated error, even though they were documented in exactly the same way as the rest. Here is an example of the complete roxygen documentation I included above one of the show methods, that did NOT generate the missing-documentation error:

    #&#39; @name show
    #&#39; @aliases show,myClass2-method
    #&#39; @docType methods
    #&#39; @rdname show-methods

Thus, I&#39;m at a loss. As you can see, I&#39;ve included the convention for aliases for S4 methods described in [the S4 documentation section of the R package manual](http://cran.r-project.org/doc/manuals/R-exts.html#Documenting-S4-classes-and-methods), namely that methods should have an alias with the following name (without space):

    generic,signature_list-method.

Somehow, this is not completely being understood by `R CMD check`.

Finally, after building the documentation using: 

    library(&quot;devtools&quot;)
    library(&quot;roxygen2&quot;)
    document(&quot;mypkgname&quot;)
    check_doc(&quot;mypkgname&quot;)

and building the package, I get functioning documentation. Any titles from a specific method&#39;s documentation winds up in the &#39;Description&#39; field, rather awkwardly. So roxygen2 obviously did something with each method&#39;s documentation and is on the right track. However, it is not enough to avoid a large and troubling warning from 
    
    &gt; R CMD check mypkgname

I&#39;ve looked at the Rd files, but I know even less about them to quickly see what&#39;s the problem is, and I anyway want to know the roxygen2 solution so that I will not have to manipulate the Rd files directly after each documentation revision.

So this is a multipart question:

1. What is the current recommended approach for both S4 generic and S4 method documentation with roxygen2?

2. Is there a good example available somewhere that shows the complete details?

3. What might be the cause, and solution, to the &lt;R CMD check mypkgname&gt; warning that documentation for most S4 methods is missing (even though the methods with &quot;missing&quot; documentation actually have had their doc parsed by roxygen2 and the resulting Rd files are at least good enough to work in the package after `R CMD build mypkgname`) ?







How to properly document S4 methods using roxygen2

For documenting classes with roxygen(2), specifying a title and description/details appears to be the same as for functions, methods, data, etc. However, slots and inheritance are their own sort of animal. What is the best practice -- current or planned -- for documenting S4 classes in roxygen2?

Due Diligence:

I found mention of an `@slot` tag in early descriptions of roxygen. 
[A 2008 R-forge mailing list post](http://lists.r-forge.r-project.org/pipermail/roxygen-devel/2008-November/000009.html) 
seems to indicate that this is dead, 
and there is no support for `@slot` in roxygen:

Is this true of roxygen2? The previously-mentioned post suggests a user should instead make their own itemized list with LaTeX markup. E.g. a new S4 class that extends the `&quot;character&quot;` class would be coded and documented like this:

    #&#39; The title for my S4 class that extends \code{&quot;character&quot;} class.
    #&#39;
    #&#39; Some details about this class and my plans for it in the body.
    #&#39;
    #&#39; \describe{
    #&#39;    \item{myslot1}{A logical keeping track of something.}
    #&#39;
    #&#39;    \item{myslot2}{An integer specifying something else.}
    #&#39; 
    #&#39;    \item{myslot3}{A data.frame holding some data.}
    #&#39;  }
    #&#39; @name mynewclass-class
    #&#39; @rdname mynewclass-class
    #&#39; @exportClass mynewclass
    setClass(&quot;mynewclass&quot;,
    	representation(myslot1=&quot;logical&quot;,
    		myslot2=&quot;integer&quot;,
    		myslot3=&quot;data.frame&quot;),
    	contains = &quot;character&quot;
    )

However, although this works, this `\describe` , `\item` approach for documenting the slots seems inconsistent with the rest of roxygen(2), in that there are no `@`-delimited tags and slots could go undocumented with no objection from `roxygenize()`. It also says nothing about a consistent way to document inheritance of the class being defined. I imagine dependency still generally works fine (if a particular slot requires a non-base class from another package) using the `@import` tag. 

So, to summarize, what is the current best-practice for roxygen(2) slots?

There seem to be three options to consider at the moment:

&gt;  - A -- Itemized list (as example above).
&gt;  - B -- `@slot` ... but with extra tags/implementation I missed. I was    unable to get @slot to work with roxygen / roxygen2 in versions where 
&gt; it was included as a replacement for the itemized list in the example 
&gt; above. Again, the example above does work with roxygen(2). 
&gt;  - C -- Some alternative tag for specifying slots, like `@param`, that    would accomplish the same thing.

I&#39;m borrowing/extending this question from a post I made to the `roxygen2` development page on [github](https://github.com/klutometis/roxygen/issues/34).


How to properly document S4 class slots using Roxygen2?

I am working with the dataset `LearnBayes`. For those that want to see the actual data: 

    install.packages(&#39;LearnBayes&#39;)

I am trying to filter out rows based on the value in the columns. For example, if the column value is &quot;water&quot;, then I want that row. If the column value is &quot;milk&quot;, then I don&#39;t want it. Ultimately, I am trying to filter out all individuals who&#39;s Drink column is &quot;water&quot;.




Filtering a data frame by values in a column

It would be helpful if someone can illustrate this with a simple example?

Also, where would it be useful to use `parent.frame()` instead of `parent.env()` and vice versa.



What is the difference between parent.frame() and parent.env() in R; how do they differ in call by reference?

Say I have a `data.frame` object:

    df &lt;- data.frame(name=c(&#39;black&#39;,&#39;black&#39;,&#39;black&#39;,&#39;red&#39;,&#39;red&#39;),
                     type=c(&#39;chair&#39;,&#39;chair&#39;,&#39;sofa&#39;,&#39;sofa&#39;,&#39;plate&#39;),
                     num=c(4,5,12,4,3))

Now I want to count the number of rows (observations) of for each combination of `name` and `type`. This can be done like so:

    table(df[ , c(&quot;name&quot;,&quot;type&quot;)])

or possibly also with `plyr`, (though I am not sure how).

However, how do I get the results incorporated into the original data frame?  So that the results will look like this:

    df
    #    name  type num count
    # 1 black chair   4     2
    # 2 black chair   5     2
    # 3 black  sofa  12     1
    # 4   red  sofa   4     1
    # 5   red plate   3     1

where `count` now stores the results from the aggregation.

A solution with `plyr` could be interesting to learn as well, though I would like to see how this is done with base R.

Count number of rows per group and add result to original data frame

I wonder how to add regression line equation and R^2 on the `ggplot`. My code is:

    library(ggplot2)

    df &lt;- data.frame(x = c(1:100))
    df$y &lt;- 2 + 3 * df$x + rnorm(100, sd = 40)
    p &lt;- ggplot(data = df, aes(x = x, y = y)) +
                geom_smooth(method = &quot;lm&quot;, se=FALSE, color=&quot;black&quot;, formula = y ~ x) +
                geom_point()
    p

Any help will be highly appreciated.


Add regression line equation and R^2 on graph

In a ```data.frame``` (or ```data.table```), I would like to &quot;fill forward&quot; NAs with the closest previous non-NA value. A simple example, using vectors (instead of a `data.frame`) is the following:

    &gt; y &lt;- c(NA, 2, 2, NA, NA, 3, NA, 4, NA, NA)

I would like a function `fill.NAs()` that allows me to construct `yy` such that:

    &gt; yy
    [1] NA NA NA  2  2  2  2  3  3  3  4  4

I need to repeat this operation for many (total ~1 Tb) small sized `data.frame`s (~30-50 Mb), where a row is NA is all its entries are. What is a good way to approach the problem? 

The ugly solution I cooked up uses this function:

    last &lt;- function (x){
        x[length(x)]
    }    
    
    fill.NAs &lt;- function(isNA){
	if (isNA[1] == 1) {
		isNA[1:max({which(isNA==0)[1]-1},1)] &lt;- 0 # first is NAs 
												  # can&#39;t be forward filled
	}
	isNA.neg &lt;- isNA.pos &lt;- isNA.diff &lt;- diff(isNA)
	isNA.pos[isNA.diff &lt; 0] &lt;- 0
	isNA.neg[isNA.diff &gt; 0] &lt;- 0
	which.isNA.neg &lt;- which(as.logical(isNA.neg))
	if (length(which.isNA.neg)==0) return(NULL) # generates warnings later, but works
	which.isNA.pos &lt;- which(as.logical(isNA.pos))
	which.isNA &lt;- which(as.logical(isNA))
	if (length(which.isNA.neg)==length(which.isNA.pos)){
		replacement &lt;- rep(which.isNA.pos[2:length(which.isNA.neg)], 
									which.isNA.neg[2:max(length(which.isNA.neg)-1,2)] - 
									which.isNA.pos[1:max(length(which.isNA.neg)-1,1)])		
		replacement &lt;- c(replacement, rep(last(which.isNA.pos), last(which.isNA) - last(which.isNA.pos)))
	} else {
		replacement &lt;- rep(which.isNA.pos[1:length(which.isNA.neg)], which.isNA.neg - which.isNA.pos[1:length(which.isNA.neg)])		
		replacement &lt;- c(replacement, rep(last(which.isNA.pos), last(which.isNA) - last(which.isNA.pos)))
	}
	replacement
    }


The function `fill.NAs` is used as follows:

    y &lt;- c(NA, 2, 2, NA, NA, 3, NA, 4, NA, NA)
    isNA &lt;- as.numeric(is.na(y))
    replacement &lt;- fill.NAs(isNA)
    if (length(replacement)){
	which.isNA &lt;- which(as.logical(isNA))
	to.replace &lt;- which.isNA[which(isNA==0)[1]:length(which.isNA)]
	y[to.replace] &lt;- y[replacement]
    } 
***Output***

    &gt; y
    [1] NA  2  2  2  2  3  3  3  4  4  4

... which seems to work. But, man, is it ugly! Any suggestions?


Replacing NAs with latest non-NA value

How can I list the distinct values in a vector where the values are replicative? I mean, similarly to the following SQL statement:

    SELECT DISTINCT product_code
    FROM data

List distinct values in a vector in R

R&#39;s `duplicated` returns a vector showing whether each element of a vector or data frame is a duplicate of an element with a smaller subscript. So if rows 3, 4, and 5 of a 5-row data frame are the same, `duplicated` will give me the vector 

    FALSE, FALSE, FALSE, TRUE, TRUE

But in this case I actually want to get 

    FALSE, FALSE, TRUE, TRUE, TRUE

that is, I want to know whether a row is duplicated by a row with a **larger** subscript too.

Content Type	Original Author	Original Content on Stackoverflow
Question	Concerned_Citizen	View Question on Stackoverflow
Solution 1 - R	Brian Diggs	View Answer on Stackoverflow
Solution 2 - R	pbatey	View Answer on Stackoverflow
Solution 3 - R	Seyma Kalay	View Answer on Stackoverflow
Solution 4 - R	Krutik	View Answer on Stackoverflow

Error in if/while (condition) {: missing Value where TRUE/FALSE needed

R Problem Overview

R Solutions

Solution 1 - R

Solution 2 - R

Solution 3 - R

Solution 4 - R

How to split strings over multiple lines in Bash?

Center HTML Input Text Field Placeholder

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