error: '__pred' cannot be used as a function - c++

Question

I can't find what I'm doing wrong here. The function eta does what I ask but when I use it in the loop I get the attached error.
bool eta(map<string, TLorentzVector> map_jets, string jet){
return( fabs(map_jets[jet].PseudoRapidity()) > 2.5 );
}
and then
vector<pair<string,double> > jets_pt( vec_jets.size() );
for( vector<pair<string,double> >::iterator it = jets_pt.begin(); it != jets_pt.end(); ++it)
jets_pt.erase(remove_if(jets_pt.begin(),jets_pt.end(),eta(map_jets,it1->first)),jets_pt.end);
I get the error
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h: In function '_OutputIterator std::remove_copy_if(_InputIterator, _InputIterator, _OutputIterator, _Predicate) [with _InputIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _OutputIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _Predicate = bool]':
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:1291: instantiated from '_ForwardIterator std::remove_if(_ForwardIterator, _ForwardIterator, _Predicate) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _Predicate = bool]'
/misc/cdf/gbertoli/hww/Diboson_v20_taus/Ana/src/Functions.cc:25: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:1216: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h: In function '_RandomAccessIterator std::__find_if(_RandomAccessIterator, _RandomAccessIterator, _Predicate, std::random_access_iterator_tag) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _Predicate = bool]':
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:338: instantiated from '_InputIterator std::find_if(_InputIterator, _InputIterator, _Predicate) [with _InputIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _Predicate = bool]'
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:1287: instantiated from '_ForwardIterator std::remove_if(_ForwardIterator, _ForwardIterator, _Predicate) [with _ForwardIterator = __gnu_cxx::__normal_iterator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>*, std::vector<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double>, std::allocator<std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, double> > > >, _Predicate = bool]'
/misc/cdf/gbertoli/hww/Diboson_v20_taus/Ana/src/Functions.cc:25: instantiated from here
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:260: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:264: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:268: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:272: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:280: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:284: error: '__pred' cannot be used as a function
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algo.h:288: error: '__pred' cannot be used as a function
mv: cannot stat `/misc/cdf/gbertoli/hww/Diboson_v20_taus/tmp/Linux2.6-GCC_4_1/Ana/srt_dep_tmp.27294': No such file or directory
gmake[2]: *** [/misc/cdf/gbertoli/hww/Diboson_v20_taus/tmp/Linux2.6-GCC_4_1/Ana/libAna-shared/Functions.o] Error 1
gmake[1]: *** [src.lib] Error 2
gmake: *** [Ana.all] Error 2

Answer 1

First off, the only valid signature for remove_if takes a single function as the predicate argument:
jets_pt.erase(std::remove_if(jets_pt.begin(), jets_pt.end(), eta),
jets_pt.end());
This means that eta must be a function returning bool and taking precisely one argument whose type is the value type of the container:
bool eta(const std::pair<string, double> & p)
{
// do something useful with p
}
If this doesn't fit your bill because you need additional state information in the predicate, then you need to make it a function object:
struct Eta
{
const std::map<string, TLorentzVector> & map_jets;
Eta(const std::map<string, TLorentzVector> & m) : map_jets(m) { }
bool operator()(const std::pair<string, double> & p) const
{
std::map<string, TLorentzVector>::const_iterator it = map_jets.find(p->second);
return it == map_jets.end() ?
false :
std::fabs(it->second.PseudoRapidity()) > 2.5;
}
};
Now you have to use remove_if with an instance of Eta:
jets_pt.erase(std::remove_if(jets_pt.begin(), jets_pt.end(), Eta(map_jets)),
jets_pt.end()); // ^^^^^^^^^^^^^
Note that your use of the for loop is extremely suspicious; you should double-check that.

Answer 2

std::remove_if takes a value of the contained type (bool pred (container::value_type), or a functor which overloads operator() appropriately).
For std::map, you have to do it like explained here remove_if equivalent for std::map .

Answer 3

You're passing a bool (the results of calling eta) to remove_if as
the third argument. You need to pass it a predicate: a pointer to a
function taking a single argument and returning something which can be
converted to a bool, or a functional object. In the error messages,
__pred is your third argument; remove_if calls it here with a
pair<string, double>, and expects a bool in return. You have to
provide something which can be called like this. (You might want to
look into boost::bind.)
And BTW: passing a map by value to eta might not be a good idea.
It's going to slow things down considerably if the map is big.