Databases
StackOverflow2013
Postsdbo
POCount column length of data.table, column name is provided from second data.table
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POCount column length of data.table, column name is provided from second data.table
    primarykey
    data
    text
    <p>I have a data.table, let's say test.dt, with a column called "id". The rows of column "id" refer to the column headers of a second data.table, say counts.dt. I would like to provide the length of each column in counts to match up with the corresponding row id in the original test.dt. For example: </p> <pre><code>test &lt;- function() { library(data.table) test.dt &lt;- data.table(id=c("a","b","c"),other=1:3) counts.dt &lt;- data.table(a=c(1,NA,NA,NA),b=c(1,1,NA,NA),c=c(1,1,1,1),d=1:4,e=1:4) print(counts.dt) test.dt&lt;-test.dt[,count:=sum(!is.na(counts.dt[,id]))] print(test.dt) } </code></pre> <p>Which returns: counts.dt as expected:</p> <pre><code> a b c d e 1: 1 1 1 1 1 2: NA 1 1 2 2 3: NA NA 1 3 3 4: NA NA 1 4 4 </code></pre> <p>However, test.dt seems to count not the number of non-NA elements in the columns of counts.dt, but the length of test.dt resulting in:</p> <pre><code> id other count 1: a 1 3 2: b 2 3 3: c 3 3 </code></pre> <p>What I would like, is a table like:</p> <pre><code> id other count 1: a 1 1 2: b 2 2 3: c 3 4 </code></pre> <p>Thoughts?</p> <p>I have tried making my "sum" statement more complex with different eval functions with the same results. I haven't been able to find an answer to this particular question; any help or redirection to a similar question would be greatly appreciated. </p> <p><em><strong>UPDATE</em></strong>: My actual data had more longer text strings as IDs, using the answer as shown resulted in the following error: </p> <pre><code>Error in Math.factor(j) : abs not meaningful for factors </code></pre> <p>However, I was able to get things moving with the following:</p> <pre><code>get.length&lt;-function(x){return(as.character(x))} test.dt&lt;-test.dt[,count:= sum(!is.na(counts.dt[,get.length(id),with=FALSE]),na.rm=TRUE),by=id] </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USDocuemada
    1. USDocuemada
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POCount column length of data.table, column name is provided from second data.table
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POCount column length of data.table, column name is provided from second data.table
      1. USDocuemada
      1. VTFavorite
    1. This table or related slice is empty.
 

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