R: how to sample rows with custom frequencies [closed] - r

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I have a data frame in R that has two columns, one with last names, the other with the frequency of each last name. I would like to randomly select last names based on the frequency values (0 -> 1).
So far I have tried using the sample function, but it doesn't allow for specific frequencies for each value. Not sure if this is possible :/

df1 <- data.frame(names = c("John","Mary"),freq=c(0.2,0.8))
df1
# names freq
# 1 John 0.2
# 2 Mary 0.8
set.seed(1)
sample100 <- sample(
x = df1$names,
size = 100,
replace=TRUE,
prob=df1$freq)
table(sample100)
# sample100
# John Mary
# 17 83

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Dividing all integers of a column in R [closed]

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I am trying to divide all integers in a column with another integer. I have a database with a column that has integers that go above 1*10^20. Because of this my plots are way to big. I need to normalize the data to have a better understanding what is going on. For example, the data that I have:
[x][Day] [Amount]
[1] 1 1 23440100
[2] 2 2 41231020
[3] 3 3 32012010
I am using a data.frame for my own data, so here you have the data frame for the data above
x <- c(1,2,3)
day <- c(1,2,3)
Amount <- c(23440100, 41231020, 32012010)
my.data <- data.frame(x, day, Amount)
I tried using another answer, provided here, but that doesn't seem to work.
The code that I tried:
test <- my.data[, 3]/1000
Hope someone can help me out! Cheers, Chester
I guess you are looking for this?
my.data$Amount <- my.data$Amount/1000
such that
> my.data
x day Amount
1 1 1 23440.10
2 2 2 41231.02
3 3 3 32012.01
Use mutate from dplyr
Since you're using a data.frame, you can use this simple code:
library(dplyr)
mutated.data <- my.data %>%
mutate(Amount = as.integer(Amount / 1000))
> mutated.data
x day Amount
1 1 1 23440.10
2 2 2 41231.02
3 3 3 32012.01
Hope this helps.

Replace row values by max values in the group [closed]

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I have a data frame look like this
a <- c(10,NA,30,40,NA,60,70,80,90,90,80,90,10,40)
b <- c(l,k,l,l,k,l,l,l,k,k,l,l,k,l)
c <- c(1,1,1,2,2,2,2,2,3,3,3,4,4,4)
I want to group data frame by column 'b' and 'c', then replace row values in 'a' column by max value of each group. For example: the 1st and 2nd of the 'a' column would be replaced by 30. Here is my code:
df%>%group_by(b, c)%>%mutate(a = max(a, na.rm = TRUE))
Other values are replaced by max value but not NA. I don't know why mutatefunction rewrite NA by inf. Here is the result I have with my code:
a <- c(30,inf,30,80,inf,80,80,80,90,90,90,90,10,90)
But I want it like this:
a <- c(30,30,30,80,80,80,80,80,90,90,90,90,10,90)
Assuming your data are:
Tuong_df <- data.frame(
c(10,NA,30,40,NA,60,70,80,90,90,80,90,10,40),
c("l","l","l","l","l","l","l","l","k","k","k","k","k","k"),
c(1,1,1,2,2,2,2,2,3,3,3,4,4,4))
names(Tuong_df) <- c("Var1","Var2","Var3")
You have to run the following code:
Tuong_df_mod <- Tuong_df %>%
group_by(Var2,Var3) %>%
mutate(Var1=max(Var1,na.rm=TRUE))
Anyway, for the near future, it should be better if you release reproducible code.

How to add a column with constant observation and another variable with consecutive numbers with a character in R [closed]

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Closed 6 years ago.
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I want to add a first column with consecutive numbers with characters in a existing data frame.
I use the following code. It does not work.
df$VARNAME_ <- paste0('COL', 1:5)(df)
I want to it look like this.
VARNAME_ old_var1 old_var2
COL1 1 2
COL2 1 2
COL3 1 2
COL4 1 2
COL5 1 2
Thanks in advance.
I am Sorry that I asked a stupid question. And now I figure out.
The solution is as following.
actual_df<-data.frame(df)#transfer matrix a to data frame
actual_df<-cbind(VARNAME_=paste0('COL', 1:5),actual_df) #add COL1~COL5 in the first column
actual_df<-cbind(ROWTYPE_ = 'PROX', actual_df) #Add a variable with constant observations in first column. Now the previous column become second one.
df$VARNAME_ = paste0('COL', 1:5)
will work

How to subset a dataframe based on one column level? [closed]

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Closed 5 years ago.
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I would like to subset a df based on one level in a column, i.e. keep all rows that only contain this unique level within a column.
For this example I want a df with all columns that meet the criteria "blue" in column "D" without losing information. Whether that is subset, filter, etc.
A B C D E
1 2 3 "blue" 8
7 4 6 "red" 5
5 9 1 "green" 2
I have tried the variations of the following script:
newdf = subset(df, D == "blue")
newdf = subset(df, levels(D) == "blue")
This should work:
newdf = df[df$D == "blue", ]

WeiRd: R does not find value but it's just there [closed]

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This question was caused by a typo or a problem that can no longer be reproduced. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers.
Closed 2 years ago.
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Trying to merge two data frames, using a variable called hash_id. For some reason R does not recognize the hash-id's in one of the data frames, while it does so in the other.
I have checked and I just don't get it. See below how I checked:
> head(df1[46],1) # so I take the first 'hash-id' from df1
# hash_id
# 1 abab123123
> which(df2 == "abab123123", arr.ind=TRUE) # here it shows that row 6847 contains a match
# row col
# [1,] 6847 32`
> which(df1 == "abab123123", arr.ind=TRUE) # and here there is NO matching value!
# row col
#
One possibility is trailing or leading spaces in the concerned columns for one of the datasets. You could do:
library(stringr)
df1[, "hash_id"] <- str_trim(df1[,"hash_id"])
df2[, "hash_id"] <- str_trim(df2[, "hash_id"])
which(df1[, "hash_id"]=="abab123123", arr.ind=TRUE)
which(df2[, "hash_id"]=="abab123123", arr.ind=TRUE)
Another way would be use grep
grepl("\\babab123123\\b", df1[,"hash_id"])
grepl("\\babab123123\\b", df2[,"hash_id"])

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