<p>If I understood correctly, your step 2 involves creating a project containing 200,000 cells containing 200,000 elements each, i.e. 200,000^2 = 40 billion elements &lt;- it is way too much to deal with for OpenRefine.</p>

<p>Then you would have to do 40 billion more calculations to compare each of your 200,000 dates with the other 200,000. At the rate of 1 millisecond per calculation, this would make 1111 hours of calculation, or 462 days...</p>

<p>You definitely need another tool than OpenRefine (<a href="https://recordlinkage.readthedocs.io/en/latest/about.html" rel="nofollow noreferrer">example in Python</a>). And in any case, you will need to develop a technique to reduce the number of comparisons. The most common in this type of case is <a href="https://arxiv.org/abs/1407.3191" rel="nofollow noreferrer">blocking</a>. It consists in comparing only values that are already close enough (for example only dates with the same year). But it is difficult to suggest a strategy without knowing your data. </p>
How to compare cells from different rows within the same project in OpenRefine
<p>I have a set of data with a column named <code>START</code> containing date values.</p>
<p>Is there a way to compare the <code>START</code> value of a row against all other <code>START</code> values inside the project?</p>
<p>I'd like to create a new column with a message like this <code>&quot;Rows n° x,y,...,z contains greater START values&quot;.</code></p>
<p>I've tried the following using <code>&quot;cell.cross&quot;</code> function to compare two projects (actually the same project) but it seems to be too resource and time consuming:</p>
<pre><code>1. create a new column COMPARE with a fixed value
2. use &quot;cell.cross&quot; function against column COMPARE to import in every row all the START values of the project, collapsed in a new column named ALL_START_VALUES
3. compare START value against the array in ALL_START_VALUES and generate log
</code></pre>
<p>Too bad, my 200k rows project freezes during step n°2.</p>
<p>This is what i'd like to obtain:</p>
<blockquote>
<p>ROW | START      | LOG</p>
<p>0 | 2019-01-<strong>01</strong>T00:00:00Z | Rows n° 1,2 contain greater START values</p>
<p>1 | 2019-01-<strong>02</strong>T00:00:00Z | Rows n° 2 contain greater START values</p>
<p>2 | 2019-01-<strong>03</strong>T00:00:00Z |</p>
</blockquote>