Relating dataframes with If statements and loops - r

Question

I have the following dataframes:
df1 <- data.frame(ProjectID=c(10,11,12,13),
Value1=c(101.25,102.85,102.95,103.15),
Value2=c(103.58,104.27,104.68,106.01))
df2 <- data.frame(ProjectID=c(10,10,11,11,11,12,13,13),
Value3=c(98.32,102.58,99.66,103.47,105.63,105.18,102.02,104.98))
I would like to create the following column df1$Value4, which pulls from df2$Value3 if the following conditions are met:
The ProjectIDs must match in df1 & df2
df2$Value3 must be in between df1$Value1 & df1$Value2
If the above 2 conditions are not met, input ""
I'm interested in using loops and if statements to accomplish this if possible. Any help is most appreciated.
The output should look like this:
df1 <- data.frame(ProjectID=c(10,11,12,13),
Value1=c(101.25,102.85,102.95,103.15),
Value2=c(103.58,104.27,104.68,106.01),
Value4=c(102.58,103.47,"",104.98))

Answer 1

This will merge the two data.frame and then remove the rows where Value3 is not between Value1 and Value2. The second merge will add back rows from df1 that do not satisfy the previous condition. And finally the last command will rename the column.
df3 <- merge(df1, df2)
df3 <- df3[df3$Value1 < df3$Value3 & df3$Value3 < df3$Value2, ]
df3 <- merge(df1, df3, all.x = TRUE)
colnames(df3)[colnames(df3) == "Value3"] <- "Value4"
df3
ProjectID Value1 Value2 Value4
1 10 101.25 103.58 102.58
2 11 102.85 104.27 103.47
3 12 102.95 104.68 NA
4 13 103.15 106.01 104.98

Answer 2

Doing it by loops and logic statements makes the code a bit long. I am sure dplyr statements could shorten this up. Additionally, I am not sure what you plan on doing with the output, but R will convert the Value4 field to a character data type because of the "". If you wish to do any kind of data manipulation afterwards, I would suggest using NAs instead of "". To do this, just replace the "" with NA in the code below. Anyway, the code you are looking for is:
df1$Value4 <- ""
for (i in 1:nrow(df1)) {
match_df2 <- df2$Value3[df2$ProjectID == df1$ProjectID[i]]
btwn <- c(df1$Value1[i], df1$Value2[i])
btwn <- sort(btwn)
match_v12 <- c()
for (j in 1:length(match_df2)) {
if (match_df2[j] >= btwn[1] & match_df2[j] <= btwn[2]) {
match_v12 <- rbind(match_v12, match_df2[j])
}
}
if (length(match_v12) == 0) {
df1$Value4[i] <- ""
} else {
df1$Value4[i] <- max(match_v12)
}
}
First create the empty Value4 field in df1 and populate it with an empty character string. The first loop statement will loop through each projectID in df1 and determine the matching location of ProjectIDs in df2. Those matching locations are stored in match_df2. Next, Value1 and Value2 are put into a vector called btwn to allow for sorting. In the example you gave, Value1 is always less than Value2, but I am not sure if that is always the case.
The next for loop checks to see if the matched Value3 values are in between Value1 and Value2. If Value3 is in between, it adds Value3 to a vector called match_v12. If multiple matches are found for a single ProjectID, than I assumed the max of the matched Value3s. You can change this to anything you like, I just put something down. Finally, if no matches are found, produce "" (This last part is redundant, but overall, not bad code).
Hope this helps