Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>There's a lot that needs explaining here. Let's start with the simplest case. In your first example, all you need is:</p> <pre><code>mydf$z &lt;- with(mydf,ifelse(x == 1,0,n)) </code></pre> <p>An equivalent <code>ddply</code> solution might look like this:</p> <pre><code>ddply(mydf,.(x),transform,z = ifelse(x == 1,0,n)) </code></pre> <p>Probably your biggest source of confusion is that you seem to not understand what is being passed as arguments to functions within <code>ddply</code>.</p> <p>Consider your first attempt:</p> <pre><code>k &lt;- function(x) { mydf$z &lt;- ifelse(x == 1, 0, mydf$n) return (mydf) } </code></pre> <p>The way <code>ddply</code> works is that it splits <code>mydf</code> up into several, smaller data frame, based on the values in the column <code>x</code>. That means that each time <code>ddply</code> calls <code>k</code>, the argument passed to <code>k</code> is <em>a data frame</em>. Specifically, a subset of you primary data frame.</p> <p>So within <code>k</code>, <code>x</code> is a subset of <code>mydf</code>, with all the columns. You should not be trying to modify <code>mydf</code> from within <code>k</code>. Modify <code>x</code>, and then return the modified version. (If you must, but the options I displayed above are better.) So we might re-write your <code>k</code> like this:</p> <pre><code>k &lt;- function(x) { x$z &lt;- ifelse(x$x == 1, 0, x$n) return (x) } </code></pre> <p>Note that you've created some confusing stuff by using <code>x</code> as both an argument to <code>k</code> <em>and</em> as the name of one of our columns.</p>
    singulars
    1. This table or related slice is empty.
    1. POR ddply, applying if and ifelse functions
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USjoran
    1. USjoran
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POR ddply, applying if and ifelse functions
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO@baptiste I know. That's why my first option just used `ifelse`. But they might as well know how to use `ddply` while we're at it.
      singulars
      1. PO
      1. USjoran
    2. COi knew you knew, which you knew I knew; the new version explains more
      singulars
      1. PO
      1. USbaptiste
    3. CO@baptiste Sorry, I didn't know that I didn't know that you knew that I knew, you know?
      singulars
      1. PO
      1. USjoran
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload