R function for looping over a string with unique values - r

I am working on a project where I have to download more than 10 million records on a relatively small server. So instead of just downloading the entire dataset, I have to download it in smaller sections. I am trying to create a loop that will call batches of the data based on date. I'm used to coding in Stata where you can call a local by using `x' or some variant within a string. However, I can't find a way to do this in R. Below is a small piece of the code I'm using. Basically, whenever I try to run this 'val' and 'val2' aren't updating with the dates in the defined lists so the output literally just reads as if the server is trying to search between 'val' and 'val2' instead of between '20190101' and '20190301'. Any suggestions for how to fix this are greatly appreciated!
x<-c(20190101, 20190301)
y<-c(20190301, 20190501)
foreach (val=x, val2=y) %do% {
data<-DBI::dbGetQuery(myconn, "SELECT * FROM .... WHERE (DATE BETWEEN 'val' AND 'val2')")
}

With a basic loop
x<-c(20190101, 20190301)
y<-c(20190301, 20190501)
data_all = c()
for(i in 1:length(x)){
query = paste0("SELECT * FROM .... WHERE (DATE BETWEEN '",
x[i], "' AND '", y[i], "')")
data <- DBI::dbGetQuery(myconn, query)
data_all = rbind(data_all, data)
}

With sprintf you can construct the query and use lapply + do.call to combine the results into one dataframe.
x<-c(20190101, 20190301)
y<-c(20190301, 20190501)
input <- sprintf("SELECT * FROM .... WHERE (DATE BETWEEN '%s' AND '%s')", x, y)
result <- do.call(rbind, lapply(input, function(x) DBI::dbGetQuery(myconn, x)))
Using purrr::map_df is a bit shorter.
result <- purrr::map_df(input, ~DBI::dbGetQuery(myconn, .x))

Related

How to lookup data and print values based on criteria in R?

So I have a csv file that has 12 columns of data, what I want to do is get specific values from the CSV file based on the desired criteria
A snip of the data is provided, so I have this list of Maps:
Maps <- c("Nuke","Vertigo","Inferno","Mirage","Train","Overpass","Dust2")
The goal is to get CTWinProb & TWinProb values for each of the maps in the Map list, e.g.
CTWinProbs;
Nuke = 0.5758
Dust2 = 0.4965
Inferno = 0.4885
etc and vice versa for TWinProb
So far I have been using sqldf library which is very tedious, this is what I am currently doing:
T1NukeCT <- sqldf("select CTWinProb from Team1 where MapName like '%Nuke%'")
which outputs T1NukeCT = 0.5758
and repeating for each Map and then again for TWinProb
I am sure there is an easier way, just quite new to using R so am not 100% on the best method here or how to go about doing it in a less tedious manner
You may use a WHERE IN (...) clause:
Maps <- c("Nuke","Vertigo","Inferno","Mirage","Train","Overpass","Dust2")
where_in <- paste0("('", paste(Maps, collapse="','"), "')")
sql <- paste0("SELECT CTWinProb FROM Team1 WHERE MapName IN ", where_in)
T1NukeCT <- sqldf(sql)
To be clear, the SQL query generated by the above script is:
SELECT CTWinProb
FROM Team1
WHERE MapName IN ('Nuke','Vertigo','Inferno','Mirage','Train','Overpass','Dust2')
What output/results are you looking for exactly?
If you want results in R, these are two simple functions to return the desired values.
They require the dplyr package to be loaded.
library(dplyr)
YourData <- read_csv("./yourfile/.csv")
CTWinFunc <- function(x){
YourData %>% filter(MapName == x) %>% pull(CTWinProb)}
TWinFunc <- function(x){
YourData %>% filter(MapName == x) %>% pull(TWinProb)}
Now CTWinFunc("Nuke") should return CTWinProb result for Nuke, ie: 0.5758
And TWinFunc("Nuke") should return TWinProb result for Nuke, ie: 0.4242
If you want to return a vector with all the results together, I guess you could use the sapply() function. Something like this...
TWins <- sapply(Maps, TWinFunc)
TWins[lengths(TWins)==0] <- NA
TWins <- unlist(TWins)
And this should give you a table with the results:
cbind(Maps, Twins)
Of course, it seems like all this data is already in the original table and you could just subset that.
YourData[,c(4,11,12)]

How to read data from a database by chunk in R?

In dplyr, if tbl is a table in a database then head(tbl) gets translated into
select
*
from
tbl
limit 6
but there doesn't seem to be a way to use the offset keyword to read data in chunks. E.g. the equivalent of
select
*
from
tbl
limit 6 offset 5
doesn't seem possible with dplyr. In dbplyr, there is a do function to let you choose a chunk_size to bring back data chunk-by-chunk.
Is that the only way to do it in R? The solution doesn't have to in dplyr or the tidyverse.
Another approach would be to construct your own offset function. This assumes your database supports it, and the function is unlikely to be transferable to databases of other types.
Something like the following:
offset_head = function(table, num, offset){
# get connection
db_connection = table$src$con
sql_query = build_sql(con = db_connection,
sql_render(table),
"\nLIMIT ", num,
"\nOFFSET ", offset
)
return(tbl(db_connection, sql(sql_query)))
}
The way I have done this in dbplyr is based on the addition of a reference/ID column:
my_tbl = tbl(con, "table_name")
for(i in 1:100){
sub_tbl = my_tbl %>% filter(ID %% 100 == i)
# further processing using 'sub_tbl'
...
}
If you add a row number to your dataset, then your filter could be replaced by filter(LowerBound < row_number & row_number < UpperBound).

How can we bulk insert data in SQLServer without creating a text file from RODBC package?

This question is the extension of this question How to quickly export data from R to SQL Server. Currently I am using following code:
# DB Handle for config file #
dbhandle <- odbcDriverConnect()
# save the data in the table finally
sqlSave(dbhandle, bp, "FACT_OP", append=TRUE, rownames=FALSE, verbose = verbose, fast = TRUE)
# varTypes <- c(Date="datetime", QueryDate = "datetime")
# sqlSave(dbhandle, bp, "FACT_OP", rownames=FALSE,verbose = TRUE, fast = TRUE, varTypes=varTypes)
# DB handle close
odbcClose(dbhandle)
I have tried this approach also, which is working beautifully and I have gained significant speed as well.
toSQL = data.frame(...);
write.table(toSQL,"C:\\export\\filename.txt",quote=FALSE,sep=",",row.names=FALSE,col.names=FALSE,append=FALSE);
sqlQuery(channel,"BULK
INSERT Yada.dbo.yada
FROM '\\\\<server-that-SQL-server-can-see>\\export\\filename.txt'
WITH
(
FIELDTERMINATOR = ',',
ROWTERMINATOR = '\\n'
)");
But my issue is I can NOT keep my data at rest between the transaction (Writing data to a file is not an option because of data security), so I was looking for solution if I can directly Bulk insert from memory or cache the data. Thanks for the help.
Good question - also useful in instances where the BULK INSERT permissions cannot be setup for whatever reason.
I threw together this poor man's solution a while back when I had enough data that sqlSave was too slow, but not enough to justify setting up BULK INSERT, so it does not require any data being written to a file. The primary reason that sqlSave and parameterized queries are so slow for inserting data is that each row is inserted with a new INSERT statement. Having R write the INSERT statement manually bypasses this in my example below:
library(RODBC)
channel <- ...
dataTable <- ...relevant data...
numberOfThousands <- floor(nrow(dataTable)/1000)
extra <- nrow(dataTable)%%1000
thousandInsertQuery <- function(channel,dat,range){
sqlQuery(channel,paste0("INSERT INTO Database.dbo.Responses (IDNum,State,Answer)
VALUES "
,paste0(
sapply(range,function(k) {
paste0("(",dat$IDNum[k],",'",
dat$State[k],"','",
gsub("'","''",dat$Answer[k],fixed=TRUE),"')")
})
,collapse=",")))
}
if(numberOfThousands)
for(n in 1:numberOfThousands)
{
thousandInsertQuery(channel,(1000*(n-1)+1):(1000*n),dataTable)
}
if(extra)
thousandInsertQuery(channel,(1000*numberOfThousands+1):(1000*numberOfThousands+extra))
SQL's INSERT statements written out with values will only accept up to 1000 rows at a time, so this code breaks it up into chunks (much more efficiently than one row at a time).
The thousandInsertQuery function will obviously have to be customized to handle whatever columns your data frame has - note also that there are single quotes around the character/factor columns and a gsub to handle any single quotes that might be in the character column. Other than this there are no safeguards against SQL injection attacks.
What about using DBI::dbWriteTable() function?
Example below (I am connecting my R code to AWS RDS instance of MS SQL Express):
library(DBI)
library(RJDBC)
library(tidyverse)
# Specify where you driver lives
drv <- JDBC(
"com.microsoft.sqlserver.jdbc.SQLServerDriver",
"c:/R/SQL/sqljdbc42.jar")
# Connect to AWS RDS instance
conn <- drv %>%
dbConnect(
host = "jdbc:sqlserver://xxx.ccgqenhjdi18.ap-southeast-2.rds.amazonaws.com",
user = "xxx",
password = "********",
port = 1433,
dbname= "qlik")
if(0) { # check what the conn object has access to
queryResults <- conn %>%
dbGetQuery("select * from information_schema.tables")
}
# Create test data
example_data <- data.frame(animal=c("dog", "cat", "sea cucumber", "sea urchin"),
feel=c("furry", "furry", "squishy", "spiny"),
weight=c(45, 8, 1.1, 0.8))
# Works in 20ms in my case
system.time(
conn %>% dbWriteTable(
"qlik.export.test",
example_data
)
)
# Let us see if we see the exported results
conn %>% dbGetQuery("select * FROM qlik.export.test")
# Let's clean the mess and force-close connection at the end of the process
conn %>% dbDisconnect()
It works pretty fast for small amount of data transferred and seems rather elegant if you want data.frame -> SQL table solution.
Enjoy!
Building on #jpd527 solution which I found really worth digging into...
require(RODBC)
channel <- #connection parameters
dbPath <- # path to your table, database.table
data <- # the DF you have prepared for insertion, /!\ beware of column names and values types...
# Function to insert 1000 rows of data in one sqlQuery call, coming from
# any DF and into any database.table
insert1000Rows <- function(channel, dbPath, data, range){
# Defines columns names for the database.table
columns <- paste(names(data), collapse = ", ")
# Initialize a string which will incorporate all 1000 rows of values
values <- ""
# Not very elegant, but appropriately builds the values (a, b, c...), (d, e, f...) into a string
for (i in range) {
for (j in 1:ncol(data)) {
# First column
if (j == 1) {
if (i == min(range)) {
# First row, only "("
values <- paste0(values, "(")
} else {
# Next rows, ",("
values <- paste0(values, ",(")
}
}
# Value Handling
values <- paste0(
values
# Handling NA values you want to insert as NULL values
, ifelse(is.na(data[i, j])
, "null"
# Handling numeric values you want to insert as INT
, ifelse(is.numeric(data[i, j])
, data[i, J]
# Else handling as character to insert as VARCHAR
, paste0("'", data[i, j], "'")
)
)
)
# Separator for columns
if (j == ncol(data)) {
# Last column, close parenthesis
values <- paste0(values, ")")
} else {
# Other columns, add comma
values <- paste0(values, ",")
}
}
}
# Once the string is built, insert it into SQL Server
sqlQuery(channel,paste0("insert into ", dbPath, " (", columns, ") values ", values))
}
This insert1000Rows function is used in a loop in the next function, sqlInsertAll, for which you simply define which DF you want to insert into which database.table.
# Main function which uses the insert1000rows function in a loop
sqlInsertAll <- function(channel, dbPath, data) {
numberOfThousands <- floor(nrow(data) / 1000)
extra <- nrow(data) %% 1000
if (numberOfThousands) {
for(n in 1:numberOfThousands) {
insert1000Rows(channel, dbPath, data, (1000 * (n - 1) + 1):(1000 * n))
print(paste0(n, "/", numberOfThousands))
}
}
if (extra) {
insert1000Rows(channel, dbPath, data, (1000 * numberOfThousands + 1):(1000 * numberOfThousands + extra))
}
}
With this, I am able to insert 250k rows of data in 5 minutes or so, whereas it took more than 24 hours using sqlSave from the RODBC package.

R- How to do a loop on a list and output different dataframes

I'm attempting to create a loop in R that will use a vector of dates, run them through a loop that includes a SQL query, and then generate a separate dataframe for each output. Here is as far as I've gotten:
library(RODBC)
dvect <- as.Date("2015-04-13") + 0:2
d <- list()
for(i in list(dvect)){
queryData <- sqlQuery(myconn, paste("SELECT
WQ_hour,
sum(calls) as calls
FROM database
WHERE DDATE = '", i,"'
GROUP BY 1
", sep = ""))
d[i] <- rbind(d, queryData)
}
From what I can tell, the query portion of the code runs fine since I've tested it by itself. Where I'm stumbling is the last line where I try to save the contents of each loop through the query separately with each having a label of the date that was used in the loop.
I'd appreciate any help. I've only been using R consistently for about 2 months now so I'm definitely open to alternative ways of doing this that are cleaner and more efficient.
Thanks.
I'd suggest making the SQL query a function, and use lapply to apply it and return your result as a list.
userSQLquery = function(i) {
sqlQuery(myconn, paste("SELECT
WQ_hour,
sum(calls) as calls
FROM database
WHERE DDATE = '", i,"'
GROUP BY 1
", sep = ""))
}
dvect = as.Date("2015-04-13") + 0:2
d = as.list(1:length(dvect))
names(d) = dvect
lapply(d, userSQLquery)
I have very little experience with SQL though, so this may not work. Maybe it could start you off?
Looks like a job for lapply (lapply documentation)instead of a for loop. (In R it's often good to avoid a for loop by using a vectorization.)
If you want each date to return a separate data frame, and then have each data frame labelled with the original date, try:
dates <- c("Jan 1", "Oct 31", "Dec 25")
queryData <- function(date){
#dummy data
return(runif(5))
}
results <- lapply(dates, queryData)
names(results) <- dates
Either use:
d[[i]] <- queryData
if you want each data.frame (query result) as a separate element in the list output d.
Or use:
d <- rbind(d, queryData)
if you want a single data.frame with all the query outputs combined. In this case you should declare d as a data.frame (i.e. d <- data.frame()).
You can also store each data.frame (i.e. the query result) with its corresponding date in a list as:
d[[i]] <- list(date = dvect[[i]], queryResult = queryData)
I think the last one is what you are looking for.

Assigning names to a dataframe via a loop in R

There appear to be some similar questions but I cannot quite get my head round them at this late hour
I am trying to manipulate a set of dataframes based on sql calls - something like this
x <- c(3,9,12) # x is of variable length in real world
for (i in 1:length(x)) {
nam <- paste("df",i, sep="")
assign(nam) <- sqlQuery(channel,paste(
"Select myCol from myTable where myVal =",x[i],sep=""));
}
So I am after dataframes df1,df2,df3 which I can then combine etc.
Andrie's answer below is perfect but I am having trouble extending it to two variables
myQuery <- function(t,x){
sqlQuery(channel,paste("Select myCol from myTable where myTextVal='",t,"' and myVal =", x, sep=""))
}
x <- c(3,9,12)
t <-c("00","10","12")
myData <- lapply(c(t,x), myQuery)
I am getting an 'Error in paste... argument "x" is missing, with no default'
I'm not sure if it is because there is a mix of numeric and character variables in lapply vector
but applying as.numeric /as.character in the sql statement did not seem to help
The R idiom would be to use an apply type function instead of a loop. The effect of this is that your resultant data object is a list. In this case it will be a list of data.frame objects.
Something like the following:
myQuery <- function(x){
sqlQuery(channel,paste("Select myCol from myTable where myVal =", x, sep=""))
}
x <- c(3,9,12)
t <- c("00","10","12")
myData <- lapply(c(t, x), myQuery)
You can then extract the individual data.frames with list subsetting:
myData[[1]]
EDIT. The point is that lapply will take a single vector as input. Your instruction c(t, x) combines its input into a single vector. Thus you shouldn't change myQuery - it still only takes a single input argument.
Well, the assign function needs both the name and the value as arguments:
assign(nam, sqlQuery(channel,paste("Select myCol from myTable where myVal =",x[i],sep="")))
Type ?assign to learn more...
You need mapply:
myData <- mapply(myQuery, t, x, SIMPLIFY=FALSE)
But I think better solution is to first prepare queries:
queries <- sprintf(
"Select myCol from myTable where myTextVal='%s' and myVal=%i",
t, x) # here I assume that x is integer, see ?sprintf for other formats
queries
[1] "Select myCol from myTable where myTextVal='00' and myVal=3"
[2] "Select myCol from myTable where myTextVal='10' and myVal=9"
[3] "Select myCol from myTable where myTextVal='12' and myVal=12"
And then lapply over them:
myData <- lapply(queries, function(sql) sqlQuery(channel, sql))
# could be simplified to:
myData <- lapply(queries, sqlQuery, channel=channel)

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