addition in the initial question

Dear Elisa,
Try this:
vec1<-c(33,18,13,47,30,10,6,21,39,25,40,29,14,16,44,1,41,4,15,20,46,32,38,5,31,12,48,27,36,24,34,2,35,11,42,9,8,7,26,22,43,17,19,28,23,3,49,37,50,45)
vec2<-vec1[1:26]
names(vec2)<-LETTERS[1:26]
label1<-unlist(lapply(mapply(c,lapply(seq(0,45,5),function(x) x),lapply(seq(5,50,5),function(x) x),SIMPLIFY=FALSE),function(i) paste(i[1],"<x<=",i[2],sep="")))
?dat1<-data.frame(vec2,class=cut(vec2,breaks=seq(0,50,5),labels=label1),stringsAsFactors=FALSE)
?vecNew<-cut(vec2,breaks=seq(0,50,5),labels=label1)
res<-data.frame(aggregate(row.names(dat1)~class,dat1,function(x) x),Frequency=as.data.frame(table(vecNew))[,2],stringsAsFactors=FALSE)
?names(res)[2]<- "header_elements_class"
?res
#????? class header_elements_class Frequency
#1??? 0<x<=5?????????????? P, R, X???????? 3
#2?? 5<x<=10????????????????? F, G???????? 4
#3? 10<x<=15??????????? C, M, S, Z???????? 3
#4? 15<x<=20?????????????? B, N, T???????? 2
#5? 20<x<=25????????????????? H, J???????? 2
#6? 25<x<=30????????????????? E, L???????? 3
#7? 30<x<=35?????????????? A, V, Y???????? 3
#8? 35<x<=40?????????????? I, K, W???????? 2
#9? 40<x<=45????????????????? O, Q???????? 2
#10 45<x<=50????????????????? D, U???????? 2
?str(res)
#'data.frame':??? 10 obs. of? 3 variables:
# $ class??????????????? : Factor w/ 10 levels "0<x<=5","5<x<=10",..: 1 2 3 4 5 6 7 8 9 10
# $ header_elements_class:List of 10
#? ..$ 0: chr? "P" "R" "X"
#? ..$ 1: chr? "F" "G"
#? ..$ 2: chr? "C" "M" "S" "Z"
#? ..$ 3: chr? "B" "N" "T"
#? ..$ 4: chr? "H" "J"
#? ..$ 5: chr? "E" "L"
#? ..$ 6: chr? "A" "V" "Y"
#? ..$ 7: chr? "I" "K" "W"
#? ..$ 8: chr? "O" "Q"
#? ..$ 9: chr? "D" "U"
# $ Frequency??????????? : int? 3 4 3 2 2 3 3 2 2 2


A.K.

Dear Arun,

just a small change in the initial question.
what if, instead of counting number i want to get the headers of the numbers falling in each range. finally counting those numbers to get frequencies and then drawing histograms and fitting density curve.

[HEADER] A ? B ?C ?D ?E ?F ?G ?H ?I ?J ?K ?L ?M ?N ?O ?P ?Q ?R ?S ?T ?U ?V ?W ? X Y ?Z
[VECTOR] 33 18 13 47 30 10 ?6 21 39 25 40 29 14 16 44 ?1 41 ?4 15 20 46 32 38 ?5 31 12?


classheader?of elements in each class?Frequency

0<x<=5P, R, X? ? ? ?3
5<x<=10F, G? ? ? ?2
10<x<=15 ?C, S? ? ? ?2
.....
...
...
...
45<x<=50? ? ? ?U? ? ? ?1

thankyou very much in advance

elisa