为什么每次使用dplyr的mutate时,digest函数返回相同的值? [英] Why does the digest function return the same value every time when used with dplyr's mutate?
问题描述
这是一个包含用户ID列的数据框:
Here's a data frame containing a column of user ids:
> head(df)
uid
1 14070210
2 14080815
3 14091420
为了参数,我想创建一个包含用户id的平方根的新列,另一个包含用户标识的哈希的新列。所以我这样做:
For the sake of argument, I want to create a new column containing the square root of the user id, and another new column containing a hash of the user id. So I do this:
df_mutated <- df %>%
mutate(sqrt_uid = sqrt(uid), hashed_uid = digest(uid))
... digest()来自摘要包。
... where digest() comes from the digest package.
平方根似乎起作用,摘要函数为每个用户标识返回相同的值。
While the square root appears to work, the digest function returns the same value for each user id.
> head(df_mutated)
uid sqrt_uid hashed_uid
1 14070210 3751.028 f8c4b39403e57d85cd1698d2353954d0
2 14080815 3752.441 f8c4b39403e57d85cd1698d2353954d0
3 14091420 3753.854 f8c4b39403e57d85cd1698d2353954d0
对我来说这很奇怪。没有dplyr,digest()函数会为不同的输入返回不同的值。我不了解dplyr?
This is weird to me. Without dplyr, the digest() function returns different values for different inputs. What am I not understanding about dplyr?
谢谢
推荐答案
digest()
函数没有向量化。所以如果你传递一个向量,你会得到一个整数向量的值,而不是一个向量的每个元素的摘要。由于它返回一个值,所以该值将针对您的data.frame的每一行进行回收。您可以创建自己的向量化版本
The digest()
function isn't vectorized. So if you pass in a vector, you get one value for the whole vector rather than a digest for each element of the vector. Since it returns one value, that value is recycled for each row of your data.frame. You can create your own vectorized version
vdigest <- Vectorize(digest)
df %>% mutate(sqrt_uid = sqrt(uid), hashed_uid = vdigest(uid))
# uid sqrt_uid hashed_uid
# 1 14070210 3751.028 cc90019421220a24f75b5ed5daec36ff
# 2 14080815 3752.441 9f7f643940b692dd9c7effad439547e8
# 3 14091420 3753.854 89e6666fdfdbfb532b2d7940def9d47d
与您单独传递每个向量元素时获得的匹配
which matches what you get when you pass in each vector element individually
digest(df$uid[1])
# [1] "cc90019421220a24f75b5ed5daec36ff"
digest(df$uid[3])
# [1] "89e6666fdfdbfb532b2d7940def9d47d"
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