# [C++ (gcc)], <sup><s>197</s> <s>196</s></sup> 194 bytes   

<!-- language-all: lang-cpp -->

    #import<bits/stdc++.h>
    using V=std::vector<int>;void f(V&v){V i=v,r=v;std::iota(&i[0],&*end(i),0);std::random_shuffle(&i[0],&*end(i));for(int n=rand()%v.size()+1,j=n;j;)r[i[--j]]=v[i[j%n]];v=r;}

[Try it online!][TIO-kxt0l0gi]

[C++ (gcc)]: https://gcc.gnu.org/
[TIO-kxt0l0gi]: https://tio.run/##1VHBjtMwEL33K0ZBG8WNU7q7LLB1XA6I24obuaQRyjpO69LYle2Giii/TnGcardatNyx5Ghm3ps3zxO23ydrxk6nN6LZK23TR2HNW2MrFsezzXJyMEKuIaOusli0nFmlUyHtkrRKVFBHWdiiLgNBW6xpSzxNKFtGocjnBQ6nXFaRQHiORkyXslLNd7M51PWOv2AhUisdOXmQdCBG6KqdGfGLRyi@xlsqyZYgnYs8SbZFQVsXba9kUZCWatK7J0i2O1QcUqGM1bxs/uF/MoxpSiEj1E3AHeMnWtHw6Ou3hwdnxpeZksYC25R66r6c/eA6L4BCF6yOX25Wx/vP7t4FGC7z26Afuy/HZkuw3FgzNHfXGG56DN0dhiHE8AHDu6EwZrcuw@DA9x75iOG@P0u6FYHfkZAVPzqxOTmH6ah/3hiBOPZ1BOMDh5OBdR2elnuwIE@Y98rUwUKaQpAHz4gfOS6iPFgVgrAaFmAvlf9ScP/WsSiFcGpnj3w9bBo@QRC4zmFdaCA5yvOY/hUrBSRLuLQTWfQ/2A5eM7mSZ6if9KffrN6Va3NKfv4B "C++ (gcc) – Try It Online"  

_Added 2 bytes to fix an error._   
_Saved 3 bytes thanks to [ceilingcat](https://codegolf.stackexchange.com/users/52904/ceilingcat)!!!_   

Inputs a vector of integers.   
Randomly shuffles a random subgroup of the elements in place.