If a text string contains something then return something in R

Question

consider I have a df :

Product                                   Category   
Bill Payment for Torrent Power Limited    
Recharge of Videocon d2h DTH              
Bill Payment of Airtel Mobile
Recharge of Idea Mobile

Now if a string contains "Bill Payment" and "Mobile" both then i want to tag its category as "Postpaid" and if a string contains "Recharge" and "Mobile" i want to tag it as "Prepaid".

I am a beginner in R so an easiest way would be appreciated .

Result should be

Product                                   Category   
Bill Payment for Torrent Power Limited    NA
Recharge of Videocon d2h DTH              NA
Bill Payment of Airtel Mobile             Postpaid
Recharge of Idea Mobile                   Prepaid

Answer 1

We can use grep to find the index of 'Product' with both 'Bill Payment/Mobile' ('i1') or 'Recharge/Mobile' ('i2'). After initializing the 'Category' as NA, we replace the elements based on the index i1 and i2.

i1 <- grepl('Bill Payment', df1$Product) & grepl('Mobile', df1$Product)
i2 <- grepl('Recharge', df1$Product) & grepl('Mobile', df1$Product)
df1$Category <- NA
df1$Category[i1] <- 'Postpaid'
df1$Category[i2] <- 'Prepaid'
df1
#[1] NA         NA         "Postpaid" "Prepaid" 

Or a slightly more compact (that works with the example) option is

i1 <- grepl('.*Bill Payment.*Mobile.*', df1$Product)
i2 <- grepl('.*Recharge.*Mobile.*', df1$Product)

and do with ifelse

Answer 2

A different approach is creating a numerical index first and then adding the respective values:

indx <- (grepl('Bill Payment', df1$Product) & grepl('Mobile', df1$Product)) + 
  (grepl('Recharge', df1$Product) & grepl('Mobile', df1$Product))*2 + 1L

df1$category <- c(NA, "Postpaid", "Prepaid")[indx]

which gives:

> df1
                                 Product category
1 Bill Payment for Torrent Power Limited     <NA>
2           Recharge of Videocon d2h DTH     <NA>
3          Bill Payment of Airtel Mobile Postpaid
4                Recharge of Idea Mobile  Prepaid

You can also create this index using the more compact notation as proposed by @akrun:

indx <- grepl('.*Bill Payment.*Mobile.*', df1$Product) + 
  grepl('.*Recharge.*Mobile.*', df1$Product)*2 + 1L

Or like @nicola proposed:

tmp <- grepl('Mobile', df1$Product)
indx <- (grepl('Bill Payment', df1$Product) & tmp) + (grepl('Recharge', df1$Product) & tmp)*2 + 1L