Removing rows based on character conditions in a column - r

Question

Good morning, I have created the following R code:
setwd("xxx")
library(reshape)
##Insert needed year
url <- "./Quarterly/1990_qtrly.csv"
##Writes data in R with applicable columns
qtrly_data <- read.csv(url, header = TRUE, sep = ",", quote="\"", dec=".", na.strings=" ", skip=0)
relevant_cols <- c("area_fips", "industry_code", "own_code", "agglvl_code", "year", "qtr")
overall <- c(relevant_cols, colnames(qtrly_data)[8:16])
lq <- c(relevant_cols, colnames(qtrly_data)[17:25])
oty <- c(relevant_cols, colnames(qtrly_data)[18:42])
types <- c("overall", "lq", "oty")
overallx <- colnames(qtrly_data)[9:16]
lqx <- colnames(qtrly_data)[18:25]
otyx <- colnames(qtrly_data)[seq(27,42,2)]
###Adding in the disclosure codes from each section
disc_codes <- c("disclosure_code", "lq_disclosure_code", "oty_disclosure_code")
cols_list = list(overall, lq, oty)
denom_list = list(overallx, lqx, otyx)
##Uses a two-loop peice of code to go through data denominations and categories, while melting it into the correct format
for (j in 1:length(types))
{
cat("Working on type: " , types[j], "\n")
these_denominations <- denom_list[[j]]
type_data <- qtrly_data[ , cols_list[[j]] ]
QCEW_County <- melt(type_data, id=c(relevant_cols, disc_codes[j]))
colnames(QCEW_County) <- c(relevant_cols, "disclosure_code", "text_denomination", "value")
Data_Cat <- j
for (k in 1:length(these_denominations))
{
cat("Working on type: " , types[j], "and denomination: ", these_denominations[k], "\n")
QCEW_County_Denominated <- QCEW_County[QCEW_County[, "text_denomination"] == these_denominations[k], ]
QCEW_County_Denominated$disclosure_code <- ifelse(QCEW_County_Denominated$disclosure_code == "", 0, 1)
Data_Denom <- k
QCEW_County_Denominated <- cbind(QCEW_County_Denominated, Data_Cat, Data_Denom)
QCEW_County_Denominated$Source_ID <- 1
QCEW_County_Denominated$text_denomination <- NULL
colnames(QCEW_County_Denominated) <- NULL
###Actually writes the txt file to the QCEW folder
write.table(QCEW_County_Denominated, file="C:\\Users\\jjackson\\Downloads\\QCEW\\1990_test.txt", append=TRUE, quote=FALSE, sep=',', row.names=FALSE)
}
}
Now, there are some things I need to get rid of, namely, all the rows in my QCEW_County_Denominated dataframe where the "area_fips" column begins with the character "C", in that same column, there are also codes that start with US that I would like to replace with a 0. Finally, I also have the "industry_code" column that in my final dataframe has 3 values that need to be replaced. 31-33 with 31, 44-45 with 44, and 48-49 with 48. I understand that this is a difficult task. I'm slowly figuring it out on my own, but if anyone could give me a helpful nudge in the right direction while I'm figuring this out on my own, it would be much appreciated. Conditional statements in R is looking like it's my Achilles heel, as it's always where I begin to get confused with how its syntax differs from other statistical packages.
Thank you, and have a nice day.

Answer 1

You can remove and recode your data using regex and subsetting.
Using grepl, you can select the rows in the column area_fips that DON'T start with C.
QCEW_County_Denominated <- QCEW_County_Denominated[!grepl("^C", QCEW_County_Denominated$area_fips), ]
Using gsub, you can replace with 0 the values in the area_fips columns that start with 0.
QCEW_County_Denominated$area_fips <- as.numeric(gsub("^US", 0, QCEW_County_Denominated$area_fips))
Finally, using subsetting you can replace the values in the industry_code.
QCEW_County_Denominated$industry_code[QCEW_County_Denominated$industry_code == "31-33"] <- 31
QCEW_County_Denominated$industry_code[QCEW_County_Denominated$industry_code == "44-45"] <- 44
QCEW_County_Denominated$industry_code[QCEW_County_Denominated$industry_code == "48-49"] <- 48