doge?
See the FAQ: How to do a minimal reproducible example reprex for beginners; don't make reverse-engineering data objects an obstacle to attracting questions.
The immediate problem is that logical operators (see help(logic)
These operators act on raw, logical and number-like vectors
As @nirgrahamuk notes, vectorizing in dplyr is more fluid and succinct. It also returns a more useful object.
In using a for loop, seq_along is preferred over length and providing a "receiver" object avoids the surprise of receiving only the last value of [i].
my_coins <- c("eth","usdt","link","doge")
mdata <- data.frame(symbol = c("usdt","doge"), current_price = c(1,2))
mdata
#> symbol current_price
#> 1 usdt 1
#> 2 doge 2
result <- list()
for(i in seq_along(mdata))
if (mdata$symbol[i] %in% my_coins) result[i] = mdata$current_price[i]
unlist(result)
#> [1] 1 2
suppressPackageStartupMessages({
library(dplyr)
})
mdata %>% filter(symbol %in% my_coins)
#> symbol current_price
#> 1 usdt 1
#> 2 doge 2