You can do two-way interactions simply using `.*.` and arbitrary &lt;i&gt;n&lt;/i&gt;-way interactions writing `.^n`. `formula(g)` will tell you the expanded version of the formula in each of these cases.

I&#39;m very sorry if the question seems too basic.&lt;br/&gt;
I&#39;ve surfed entire Internet and StackOverflow for a finished solution, and did not find anything that I can understand, and can&#39;t write it myself, so have to ask it here.&lt;br/&gt;

I have a MySQL database.&lt;br/&gt;
It has a table named &quot;posted&quot;.&lt;br/&gt;
It has 8 columns.&lt;br/&gt;

I need to output this result:&lt;br/&gt;

    SELECT DISTINCT link FROM posted WHERE ad=&#39;$key&#39; ORDER BY day, month

But I need not only the &quot;link&quot; column, but also other columns for this row.&lt;br/&gt;
Like for every row returned with this query I also need to know its &quot;id&quot; in the table, &quot;day&quot; and &quot;month&quot; values etc.&lt;br/&gt;

Please tell me what should I read to make it, or how to make it.&lt;br/&gt;
Please keep it as simple as possible, as I&#39;m not an expert in MySQL.


Edit:
I tried this:

    SELECT DISTINCT link,id,day,month FROM posted WHERE ad=&#39;$key&#39; ORDER BY day, month

It doesn&#39;t work. It returns too many rows. Say there are 10 rows with same links, but different day/month/id. This script will return all 10, and I want only the first one (for this link).

MySQL - SELECT all columns WHERE one column is DISTINCT

How do I calculate the time difference in milliseconds between two timestamps in Oracle?


Calculating difference between two timestamps in Oracle in milliseconds

Suppose you are using `R` and have data stored in a data frame, `M`. Then I know that 

    g &lt;- glm(Y ~ ., data=M) 

will automatically fit a model where `Y` is the dependent variables and all other columns of `M` are the predictors. Is there an analogously simple way to additionally include every two way interaction? 

How to automatically include all 2-way interactions in a glm model in R

Suppose you are using <code>R</code> and have data stored in a data frame, <code>M</code>. Then I know that
<pre><code class="hljs language-ini">g &#x3C;- glm(Y ~ ., data=M) 
</code></pre>
will automatically fit a model where <code>Y</code> is the dependent variables and all other columns of <code>M</code> are the predictors. Is there an analogously simple way to additionally include every two way interaction?

I have a list where each element is a 5*5 matrix. Eg


    [[1]]   
               V1          V2          V3          V4          V5      
          [1,]   0.000000   46.973700   21.453500  338.547000   10.401600 
          [2,]  43.020500    0.000000  130.652000  840.526000   56.363700 
          [3,]  12.605600  173.238000    0.000000  642.075000   19.628100 
          [4,] 217.946000  626.368000  481.329000    0.000000  642.341000 
          [5,] 217.946000  626.368000  481.329000    0.000000  642.341000 
    [[2]]   
               V1          V2          V3          V4          V5      
          [1,]   0.000000   47.973700   21.453500  338.547000   10.401600 
          [2,]  143.020500    0.000000  130.652000  840.526000   56.363700 
          [3,]  312.605600  17.238000    0.000000  642.075000   19.628100 
          [4,]  17.946000  126.368000  481.329000    0.000000  642.341000
          [5,] 217.946000  626.368000  481.329000    0.000000  642.341000  
    ...


 
How can I use an apply-like function to sum matrix [1] to [n],  and return a 5*5 matrix as a result (each element is a sum of the corresponding elements in each of the matrix in the list) ?

Sum a list of matrices

R help explains `invisible()` as &quot;a function that returns a temporarily invisible copy of an object&quot;. I have difficulty understanding what `invisible()` is used for. Would you be able to explain what `invisible()` does and when this function can be useful?

I&#39;ve seen that `invisible()` is almost always used in method functions for the `print()`. Here is one example:

    ### My Method function:
    print.myPrint &lt;- function(x, ...){
      print(unlist(x[1:2]))
      invisible(x)
    }

    x = list(v1 = c(1:5), v2 = c(-1:-5) )
    class(x) = &quot;myPrint&quot;
    print(x)

I was thinking that without `invisible(x)`, I wouldn&#39;t be able to do assignment like:
   
    a = print(x)

But it&#39;s actually not the case.
So, I&#39;d like to know what `invisible()` does, where it can be useful, and finally what it&#39;s role is in the method print function above?

Thank you very much for your help.

What does the function invisible() do?

I am new to ggplot2 and have been trying to find a comprehensive list of aesthetics.  I think I understand their purpose but it is hard to know which can be used in various situations (mostly geoms?). Hadley&#39;s website occasionally lists available aesthetics on pages for individual geoms and the R doc&#39;s occasionally (though more rarely) do the same. I even found a geom for which the two do not quite match.

I searched through the comments here for an answer and even bought the book! Alas, no help.

I think it would be fantastic to have a table with all the aesthetics listed in one dimension and all the geoms (and other objects?) listed in another.  

Does anyone know of such a thing?

Is there a simple way (command) in R to list all the aesthetics that can be applied to an object?

Here&#39;s how a table might start:
     
    List           x       y       fill      size    colour   linetype . . .
    geom_point    Yes     Yes      Yes       Yes      Yes        No
    geom_abline   Yes     Yes      No        Yes      Yes       Yes
    .
    .
    .

A catalog of aesthetic definitions/parameters would be a very helpful reference as well.






Is there a table or catalog of aesthetics for ggplot2?

Apologies in advance for the simplicity of this question. I am trying to import a .dat file from a website into R with the following code:

    www = &quot;http://www.nilu.no/projects/ccc/onlinedata/ozone/CZ03_2009.dat&quot;
    data &lt;- read.delim(www, header = TRUE, sep=&quot;\t&quot;) 

I want to access the Value portion of the data.frame, however, I am unsure about the dimensions of the data.frame, if I type ncol(data) it returns 1 which I was expecting three. How do I access the &quot;third&quot; column of this data.frame? 

import dat file into R

I have a data frame which has two columns of dates in the format yyyy/mm/dd.
I am trying to calculate the number of days between these two dates for each observation within the data frame (and create a new variable with this number of days in it).

So far I have tried using the answer given here:

https://stackoverflow.com/questions/5046708/calculate-the-number-of-weekdays-between-2-dates-in-r

but editing the code so that it calculates number of total days rather than just the number of week days. This just came up with error saying:

    Error in del/by : non-numeric argument to binary operator
    In addition: Warning message:
    In Ops.factor(to, from) : - not meaningful for factors

I have also attempted using this code:

    finish &lt;- as.Date(survey$date, format=&quot;%yyyy/%mm/%dd&quot;)
    start &lt;- as.Date(survey$tx_start, format=&quot;%yyyy/%mm/%dd&quot;)
    date_diff&lt;-as.data.frame(finish-start)

with the plan of using &quot;cbind&quot; or something equivalent to combine the data frame &quot;days&quot; to my data frame &quot;survey&quot; which has data in it.

Although this does not give me any errors, the observations within the &quot;finish&quot; and &quot;start&quot; objects are all &quot;NA_real_&quot;, and the date_diff data frame therefore has all the observations listed as NA.

If someone could point me in the right direction that would be great! All the other question I have found do not seem to be dealing with dates within variables but as individual dates, and applying those techniques to variables hasn`t been working for me.


Content Type	Original Author	Original Content on Stackoverflow
Question	Macro	View Question on Stackoverflow
Solution 1 - R	MvG	View Answer on Stackoverflow

How to automatically include all 2-way interactions in a glm model in R

R Problem Overview

R Solutions

Solution 1 - R

Calculating difference between two timestamps in Oracle in milliseconds

MySQL - SELECT all columns WHERE one column is DISTINCT

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