Reading data

library(ggplot2)
t = "/Users/tuannguyen/Dropbox/_Conferences and Workshops/TDTU 2019/Datasets/PISA Data Vietnam 2015.csv"
pisa = read.csv(t)

# Six lines of data 
head(pisa)
##     School SchoolSize ClassSize STratio SchoolType  Area Region   Age
## 1 70400001        883        18  22.075          3 URBAN  SOUTH 15.58
## 2 70400001        883        18  22.075          3 URBAN  SOUTH 15.92
## 3 70400001        883        18  22.075          3 URBAN  SOUTH 15.42
## 4 70400001        883        18  22.075          3 URBAN  SOUTH 15.58
## 5 70400001        883        18  22.075          3 URBAN  SOUTH 15.92
## 6 70400001        883        18  22.075          3 URBAN  SOUTH 16.25
##   Gender PARED HISCED  WEALTH INSTSCIE JOYSCIE  ICTRES    Math    Read
## 1   Boys     9      2 -2.0697   0.9798  2.1635 -1.5244 439.923 412.290
## 2   Boys    12      4 -1.7903   1.7359  2.1635 -1.9305 406.251 409.598
## 3  Girls     9      2 -2.1942  -0.2063 -0.1808 -1.6093 414.369 384.307
## 4  Girls     5      1 -2.0301  -0.3115 -0.4318 -1.6250 468.801 459.104
## 5  Girls     9      2 -1.0522   0.7648  1.3031 -0.5305 355.432 402.435
## 6  Girls     5      1 -3.0570   0.3708  0.5094 -2.5873 458.955 483.885
##   Science
## 1 475.612
## 2 450.320
## 3 405.787
## 4 462.968
## 5 453.736
## 6 529.866

Two-axis plot

p = ggplot(data=pisa, aes(x=WEALTH))
p = p + geom_line(aes(y=Science, col="red"))
p = p + geom_line(aes(y=Read, col="blue"))
p = p + scale_y_continuous(sec.axis=sec_axis(~.*1, name="Reading Score"))
p
## Warning: Removed 15 rows containing missing values (geom_path).

## Warning: Removed 15 rows containing missing values (geom_path).