Mark Allen

This is a filter for the FeedWordPress plugin. If you don’t use FeedWordPress this plugin will not be useful to you.
I wrote this filter after seeing the same post in my database 32 times. Maybe you’ve had the same problem, and I hope this filter helps you solve it.
The filter works by hooking the “syndicated_post” action of FeedWordPress and the “save_post” action in the core of WordPress.
For each potential post from a feed, the plugin attempts to find an identical SHA1 hash of the first 1024 non-whitespace characters (stripped of HTML tags) of the post content. 
If it finds a match the post is skipped. If not, the post is processed and a hash is inserted into the post’s metadata. (Stored as key _dpf.)
NOTE: No filter is going to be 100% accurate. This filter will stop most or some duplicates, but in all likelihood, will not stop all of them. 
If you want a filter that stops all duplicates, this isn’t your solution. In my test installation I had 5 posted duplicates out of 
125 syndicated posts (4% false negative) out of a corpus of about 300 duplicates. Most of those false negatives were due to slightly different HTML markup 
in the post content itself. So my approach isn’t perfect, but it is “good enough” for me.
<h3>Important Note</h3>
This filter can only check future syndication posts. Whatever duplicates are already present in your WordPress installation you’ll have to remove/clean-up on your own.
<h3>License</h3>
Copyright (C) 2012 by Mark R. Allen 
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
<ul>
<li>Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.</li>
<li>Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.</li>
<li>Neither the name of Mark Allen nor the names of any contributors may be used to endorse or promote products derived from this software without specific prior written permission.</li>
</ul>

FeedWordPress Duplicate Post Filter

A FeedWordPress syndicated post filter that checks for duplicates before posting items from your feeds.

kwiliarty

FeedGeoMashup lets <a href="https://wordpress.org/extend/plugins/feedwordpress/" rel="ugc">FeedWordPress</a> pass GeoRSS data to <a href="https://wordpress.org/extend/plugins/geo-mashup/" rel="ugc">GeoMashup</a>. Starting with v2.0 you will find plugin options integrated into the FeedWordPress Admin UI. In particlar, you can set site-wide and feed-specific preferences to filter out posts that do not include GeoRSS data. You must have installed, activated and configured both FeedWordPress and GeoMashup.
VERY IMPORTANT: You must additionally configure FeedWordPress to “Expose syndicated posts to formatting filters.” Do this on the admin side at: Syndication > Posts & Links > Formatting > Formatting filters.
<h3>Usage</h3>
You must have FeedWordPress and GeoMashup installed, activated, and configured 
in order for Feed GeoMashup to do anything. Please see the independent 
documentation for those plugins.
VERY IMPORTANT: You must additionally configure FeedWordPress to “Expose syndicated posts to formatting filters.” Do this on the admin side at: Syndication > Posts & Links > Formatting > Formatting filters.
Once you have those pieces in place, you can activate the plugin and start 
pulling in GeoMashup maps.
Go to “Syndication > Posts & Links” in the FeedWordPress admin interface to set filtering preferences.

Feed GeoMashup

Let two great plugins play great together. Use FeedWordPress to aggregate geodata generated by GeoMashup.

FeedWordPress Duplicate Post Filter vs Feed GeoMashup