#########################################################
# EXAMPLE 1: using variables
#            In R we think of variables as 'objects'
#            A object has a name a structure a value or
#            several data values
#            
#########################################################

# a simple scalar variable for integer numbers
i<-1
# our first function call: print() can print a kinds of objects
# and it will do different things with different ojects, as you see
print(i)

# a 1-dimensional array = vector  filled with integers
# with the concatenate function c() you can create vectors
index<-c(1,2,4,8,16)
print (index)

# you can also paste thigns together into a text string
text1<-paste("i=",i)
text2<-paste("index=",index)
print(text1)
print(text2)
# But that is not what we wanted
# We see that is assuming it has to perform the pasting with all values in the vector
# and you can combine functions: i.e use the returned value to feed to a second function
# Here we use paste() inside print()
# note the last optional parameter in paste(): see a difference?
print(paste('i=',i,sep=''))
# now we use a conversion of the vector with integer number into text string 
# with as.character()
clumsy<-paste(index,collapse=',')
print(paste('index=',clumsy))

# R is recyling values: look at this way to fill a vector
index2<-rep(index,2)
clumsy<-paste(index2,collapse=',')
print(paste('index2=',clumsy))


###############################################################
# here is one of the most essential programming structures
# flow control depending on some statement that can be either TRUE or FALSE
# 'if then else that'
###############################################################

if (i>0) {
  i<-i-1
} else {
  i<-i+1
}
# if your lines get too long in the code just break it up
# BUT not inside the string (inside " " or ' ')
print (paste("what happened to your initial i?  ",
              "Now i=",i,sep=''))

# okay next we will learn the most essential options to select
# subsets from a vector
# use [] to access data

# here we wnat to get element at position 4 
print(paste("index[4]=",index2[4]))

################################################################
# try to uncomment this one here and see what happens
################################################################
#print(paste("index[0]=",index2[0]))
print(paste("index[20]=",index2[20]))

# HENCE: BE CAREFUL THAT YOUR INDEX RANE IS VALID, OTHERWISE
# UNEXPECTED THINGS CAN HAPPEN
# make sure it is in the range of 1... length(index2)

print(paste("index[2:3]",index[2:3]))



# and here is something complex but later very useful
# we can pick conditionally
isbig<-index2>4
print(paste("Big numbers in index:",paste(index2[isbig],collapse=',')))



########################################################################
# next we will look at matrices and general arrays
# data frames and lists
########################################################################