Doing yum update I get the following:
kernel-modules-extra x86_64 3.18.7-100.fc20 @updates/20
8.3 M
Installing for dependencies:
GeoIP-GeoLite-data noarch 2015.04-1.fc21 updates 347 k
GeoIP-GeoLite-data-extra noarch 2015.04-1.fc21 updates 23 M
R-core x86_64 3.1.3-1.fc21 updates 48 M
R-core-devel x86_64 3.1.3-1.fc21 updates 100 k
dleyna-connector-dbus x86_64 0.2.0-4.fc21 updates 24 k
dleyna-core x86_64 0.4.0-3.fc21 fedora 30 k
dleyna-server x86_64 0.4.0-7.fc21 updates 70 k
geoipupdate x86_64 2.2.1-2.fc21 updates 33 k
lz4 x86_64 r128-2.fc21 updates 68 k
I want to know what requires R-core as i built it myself and do not want it to be installed... There must be something I must delete...
rpm -q --whatrequires R-core might tell you.
If it doesn't it might be a library or binary dependency and so you'll need to run yum whatrequires on the various libraries/binaries listed in the output from rpm -q --provides R-core and/or rpm -ql R-core.
That being said the fact that you built R yourself isn't going to help you in this case as rpm doesn't know anything about that (nor is it likely to be installed in a location that official Fedora packages can use).
If you were to build R as an rpm yourself you might be able to get that to satisfy this dependency (whatever it is) correctly though.