问题
This question already has an answer here:
- regarding matrix comparison in R 1 answer
Say I have large datasets in R and I just want to know whether two of them they are the same. I use this often when I'm experimenting different algorithms to achieve the same result. For example, say we have the following datasets:
df1 <- data.frame(num = 1:5, let = letters[1:5])
df2 <- df1
df3 <- data.frame(num = c(1:5, NA), let = letters[1:6])
df4 <- df3
So this is what I do to compare them:
table(x == y, useNA = 'ifany')
Which works great when the datasets have no NAs:
> table(df1 == df2, useNA = 'ifany')
TRUE
10
But not so much when they have NAs:
> table(df3 == df4, useNA = 'ifany')
TRUE <NA>
11 1
In the example, it's easy to dismiss the NA as not a problem since we know that both dataframes are equal. The problem is that NA == <anything> yields NA, so whenever one of the datasets has an NA, it doesn't matter what the other one has on that same position, the result is always going to be NA.
So using table() to compare datasets doesn't seem ideal to me. How can I better check if two data frames are identical?
P.S.: Note this is not a duplicate of R - comparing several datasets, Comparing 2 datasets in R or Compare datasets in R
回答1:
Look up all.equal. It has some riders but it might work for you.
all.equal(df3,df4)
# [1] TRUE
all.equal(df2,df1)
# [1] TRUE
回答2:
As Metrics pointed out, one could also use identical() to compare the datasets. The difference between this approach and that of Codoremifa is that identical() will just yield TRUE of FALSE, depending whether the objects being compared are identical or not, whereas all.equal() will either return TRUE or hints about the differences between the objects. For instance, consider the following:
> identical(df1, df3)
[1] FALSE
> all.equal(df1, df3)
[1] "Attributes: < Component 2: Numeric: lengths (5, 6) differ >"
[2] "Component 1: Numeric: lengths (5, 6) differ"
[3] "Component 2: Lengths: 5, 6"
[4] "Component 2: Attributes: < Component 2: Lengths (5, 6) differ (string compare on first 5) >"
[5] "Component 2: Lengths (5, 6) differ (string compare on first 5)"
Moreover, from what I've tested identical() seems to run much faster than all.equal().
来源：https://stackoverflow.com/questions/19119320/how-to-check-if-two-data-frames-are-equal