I have a data frame with several columns; some numeric and some character. How to compute the sum of a specific column? I've googled for this and I see numerous functions ( sum
, cumsum
, rowsum
, rowSums
, colSums
, aggregate
, apply
) but I can't make sense of it all.
For example suppose I have a data frame people
with the following columns
people <- read(
text =
"Name Height Weight
Mary 65 110
John 70 200
Jane 64 115",
header = TRUE
)
…
How do I get the sum of all the weights?
You can just use sum(people$Weight)
.
sum
sums up a vector, and people$Weight
retrieves the weight column from your data frame.
Note - you can get built-in help by using ?sum
, ?colSums
, etc. (by the way, colSums
will give you the sum for each column).
To sum values in data.frame
you first need to extract them as a vector.
There are several way to do it:
# $ operatior
x <- people$Weight
x
# [1] 65 70 64
Or using [, ]
similar to matrix:
x <- people[, 'Weight']
x
# [1] 65 70 64
Once you have the vector you can use any vector-to-scalar function to aggregate the result:
sum(people[, 'Weight'])
# [1] 199
If you have NA values in your data, you should specify na.rm
parameter:
sum(people[, 'Weight'], na.rm = TRUE)
you can use tidyverse package to solve it and it would look like the following (which is more readable for me):
library(tidyverse) people %>% summarise(sum(weight))
如果列中有'NA'值,那么
sum(as.numeric(JuneData1$Account.Balance), na.rm = TRUE)
to order after the colsum :
order(colSums(people),decreasing=TRUE)
if more than 20+ columns
order(colSums(people[,c(5:25)],decreasing=TRUE) ##in case of keeping the first 4 columns remaining.
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