working with nested for loop with if statment - r

Question

I have a data frame of two columns first is the longitude and second is the latitude. I want to find the coordinates of the center cell.
e.g. the range is lat[31 31.5], lon[33 33.5] if the first values of two columns fulfill this condition then create the third column and put the value 31.25 and create the fourth column and put in it the value 33.25
I have tried nested for loop but it does not work
# my dataframe is cycle8 contain 166 rows and two columns
latitude<- seq(31,37,by=0.5)
longitude<- seq(33,37,by=0.5)
cycle8$latcenter<- 0
cycle8$loncenter<-0
for (m in 1:nrow(cycle8))
{
for(j in seq_along(latitude))
{
for(k in seq_along(longitude))
{
if (cycle8$lat[m]>=j && cycle8$lat[m]<=j+0.5 && cycle8$lon[m]>=k &&
cycle8$lon[m]<=k+0.5)
{
cycle8$latcenter[m]<- j+0.25
cycle8$loncenter[m]<- k+0.25
}
}
}
}
the following code will work and deliver the desired result but it is so long and requires a lot of statement typing
cycle8$latcenter<- 0
for (m in 1:nrow(cycle8))
{
if (cycle8$lat[m]>=31 && cycle8$lat[m]<=31.5 )
{
cycle8$latcenter[m]<- 31+0.25
}
else if
(cycle8$lat[m]>=31.5 && cycle8$lat[m]<=32 ){
cycle8$latcenter[m]<- 31.5+0.25
}
else if
(cycle8$lat[m]>=32 && cycle8$lat[m]<=32.5 ){
cycle8$latcenter[m]<- 32+0.25
}
else if
(cycle8$lat[m]>=32.5 && cycle8$lat[m]<=33 ){
cycle8$latcenter[m]<- 32.5+0.25
}
else if
(cycle8$lat[m]>=33 && cycle8$lat[m]<=33.5 ){
cycle8$latcenter[m]<- 33+0.25
}
else if
(cycle8$lat[m]>=33.5 && cycle8$lat[m]<=34 ){
cycle8$latcenter[m]<- 33.5+0.25
}
else if
(cycle8$lat[m]>=34 && cycle8$lat[m]<=34.5 ){
cycle8$latcenter[m]<- 34+0.25
}
else if
(cycle8$lat[m]>=34.5 && cycle8$lat[m]<=35 ){
cycle8$latcenter[m]<- 34.5+0.25
}
else if
(cycle8$lat[m]>=35 && cycle8$lat[m]<=35.5 ){
cycle8$latcenter[m]<- 35+0.25
}
else if
(cycle8$lat[m]>=35.5 && cycle8$lat[m]<=36 ){
cycle8$latcenter[m]<- 35.5+0.25
}
else if
(cycle8$lat[m]>=36 && cycle8$lat[m]<=36.5 ){
cycle8$latcenter[m]<- 36+0.25
}
else if
(cycle8$lat[m]>=36.5 && cycle8$lat[m]<=37 ){
cycle8$latcenter[m]<- 36.5+0.25
}
}

Answer 1

My solution avoids for-loops, sapply or other similiar functions. The logic behind the code is as follows: Since the ranges have decimals .50 or .00, the centered values will always be .25 or .75. This means that we simply need to replace the decimals; all decimals between .00 and.50 become.25, while the other ones become .75.
Here the code for this
# generate data
latitude <- seq(30, 32, .1)
longitude <- seq(30, 32, .1)
cycle8 <- data.frame(latitude, longitude)
# make a function that replaces decimals as explained above
lat_lon <- function(vec){
decimals <- as.character(format(vec, nsmall= 1))
decimals <- as.numeric(gsub("^.*\\.", "", decimals))
decimals <- ifelse(decimals < 5, .25, .75)
values <- as.numeric(gsub("\\..*","",vec)) + as.numeric(decimals)
return(values)
}
# apply function
cycle8$lat_center <- lat_lon(latitude)
cycle8$lon_center <- lat_lon(longitude)
# see results
cycle8
EDIT
Because you want 30.00 to be 29.75 and 30.50 to be 30.25, here is an edit. But the logic remains the same.
latitude <- seq(30, 32, .1)
longitude <- seq(30, 32, .1)
cycle8 <- data.frame(latitude, longitude)
lat_lon <- function(vec){
decimals <- as.character(format(vec, nsmall= 1))
decimals <- as.numeric(gsub("^.*\\.", "", decimals))
decimals_new <- ifelse(decimals > 5 | decimals == 0, .75, .25)
values <- as.numeric(gsub("\\..*","",vec)) + as.numeric(decimals_new)
values[decimals == 0] <- values[decimals == 0] - 1
return(values)
}
cycle8$lat_center <- lat_lon(latitude)
cycle8$lon_center <- lat_lon(longitude)
cycle8

Answer 2

# The other way of solving this question is
mydata<- c(35.666,35.4578,35.0, 33.50,32.10)
centered_value <- function(val){
a<- trunc(val)
b<- val %% 1
c<- ifelse(b/0.5 > 1, a +0.75 , ifelse(b/0.5> 1, a+0.25, ifelse(b/0.5 ==0, a-
0.25,a+0.25)))
}
d<- centered_value(mydata)
d