Convert values using a conversion table R - r

Question

I am currently running statistical models on ACT and SAT scores. To help clean my data, I want to convert the ACT scores into its SAT equivalent. I found the following table online:
ACT SAT
<dbl> <dbl>
1 36 1590
2 35 1540
3 34 1500
4 33 1460
5 32 1430
6 31 1400
7 30 1370
8 29 1340
9 28 1310
10 27 1280
I want to replace the column ACT_Composite with the number in the SAT column of the conversion table. For instance, if one row displays an ACT_Composite score of 35, I want to input 1540.
If anyone has ideas on how to accomplish this, I would greatly appreciate it.

Answer 1

In base you can you use merge directly:
#Reading score table
df <- read.table(header = TRUE, text ="ACT SAT
36 1590
35 1540
34 1500
33 1460
32 1430
31 1400
30 1370
29 1340
28 1310
27 1280")
#Setting seed to reproduce df1
set.seed(1234)
# Create a data.frame with 50 sample scores
df1 <- data.frame(ACT_Composite = sample(27:36, 50, replace = TRUE))
# left-join df1 with df with keys ACT_Composite and ACT
result <- merge(df1, df,
by.x = "ACT_Composite",
by.y = "ACT",
all.x = TRUE,
sort = FALSE)
#The first 6 values of result
head(result)
ACT_Composite SAT
1 31 1400
2 31 1400
3 31 1400
4 31 1400
5 31 1400
6 36 1590
In data.table you can you use merge
library(data.table)
#Setting seed to reproduce df1
set.seed(1234)
# Create a data.table with 50 sample scores
df1 <- data.table(ACT_Composite = sample(27:36, 50, replace = TRUE))
# left-join df1 with df with keys ACT_Composite and ACT
result <- merge(df1, df,
by.x = "ACT_Composite",
by.y = "ACT",
all.x = TRUE,
sort = FALSE)
#The first 6 values of result
head(result)
ACT_Composite SAT
1: 36 1590
2: 32 1430
3: 31 1400
4: 35 1540
5: 31 1400
6: 32 1430
Alternatively in data.table you can try also
df1 <- data.table(ACT_Composite = sample(27:36, 50, replace = TRUE))
setDT(df)# you need to convert your look-up table df into data.table
result <- df[df1, on = c(ACT = "ACT_Composite")]
head(result)
ACT_Composite SAT
1: 36 1590
2: 32 1430
3: 31 1400
4: 35 1540
5: 31 1400
6: 32 1430