r - ggplot overlay plot error, no layers in plot -

i trying overlay 2 variables on same figure ggplot2, use melt data in correct format , use following:

locations <- c("usa","uk","spain") vals_1 <- c(44,6,76) vals_2 <- c(0.2,0.9,4.1)  dat <- data.frame(locs = locations,                   method_1 = vals_1,                   method_2 = vals_2) dat2 <- melt(dat,id = "locs")  ggplot(data = dat2,        aes(x = locs, y = value, colour = variable)) 

but generates error. why state there no layers?

is class of dat2[,1] , dat2[,2] being factor? if so, should changed to? graph show string in dat2[,1] on xaxis , both variables shown in plot. point me in right direction?

amend:

after adding

geom_line()

to get

ggplot(data = dat2,        aes(x = locs, y = value, colour = variable)) +   geom_line() 

i receive following error geom_path: each group consist of 1 observation. need adjust group aesthetic?

you have tell ggplot() points connect lines. done adding group=variable inside aes().

ggplot(data = dat2,        aes(x = locs, y = value, colour = variable,group=variable)) +   geom_line()